StreamReader: Cache a single instance of StringBuilder for each reader to improve performance
StreamReader: Cache a single instance of StringBuilder for each reader to improve performance

For example, a 10MB text file previously could require ~4000
StringBuilder allocations, now only 3.

richardlford/coreclr,DickvdBrink/coreclr,mmitche/coreclr,SpotLabsNET/coreclr,roncain/coreclr,mskvortsov/coreclr,gkhanna79/coreclr,dasMulli/coreclr,taylorjonl/coreclr,naamunds/coreclr,AlexGhiondea/coreclr,manu-silicon/coreclr,lzcj4/coreclr,sperling/coreclr,bartdesmet/coreclr,sejongoh/coreclr,DickvdBrink/coreclr,iamjasonp/coreclr,krk/coreclr,geertdoornbos/coreclr,krixalis/coreclr,Lucrecious/coreclr,spoiledsport/coreclr,wkchoy74/coreclr,serenabenny/coreclr,jhendrixMSFT/coreclr,SlavaRa/coreclr,misterzik/coreclr,rartemev/coreclr,hanu412/coreclr,mskvortsov/coreclr,russellhadley/coreclr,kyulee1/coreclr,SlavaRa/coreclr,yeaicc/coreclr,russellhadley/coreclr,Djuffin/coreclr,matthubin/coreclr,GuilhermeSa/coreclr,cydhaselton/coreclr,bartonjs/coreclr,AlexGhiondea/coreclr,libengu/coreclr,shahid-pk/coreclr,iamjasonp/coreclr,James-Ko/coreclr,qiudesong/coreclr,perfectphase/coreclr,tijoytom/coreclr,ramarag/coreclr,bartdesmet/coreclr,dasMulli/coreclr,SpotLabsNET/coreclr,yeaicc/coreclr,jhendrixMSFT/coreclr,richardlford/coreclr,russellhadley/coreclr,stormleoxia/coreclr,taylorjonl/coreclr,cshung/coreclr,yizhang82/coreclr,mocsy/coreclr,ragmani/coreclr,mokchhya/coreclr,parjong/coreclr,blackdwarf/coreclr,swgillespie/coreclr,sejongoh/coreclr,tijoytom/coreclr,misterzik/coreclr,ericeil/coreclr,swgillespie/coreclr,gkhanna79/coreclr,geertdoornbos/coreclr,bartonjs/coreclr,sagood/coreclr,mmitche/coreclr,neurospeech/coreclr,shana/coreclr,bartonjs/coreclr,taylorjonl/coreclr,sejongoh/coreclr,stormleoxia/coreclr,fieryorc/coreclr,josteink/coreclr,ramarag/coreclr,schellap/coreclr,ruben-ayrapetyan/coreclr,schellap/coreclr,ragmani/coreclr,shahid-pk/coreclr,spoiledsport/coreclr,DickvdBrink/coreclr,bartonjs/coreclr,chaos7theory/coreclr,dpodder/coreclr,blackdwarf/coreclr,mocsy/coreclr,hseok-oh/coreclr,stormleoxia/coreclr,ytechie/coreclr,sperling/coreclr,krk/coreclr,libengu/coreclr,david-mitchell/coreclr,orthoxerox/coreclr,ZhichengZhu/coreclr,pgavlin/coreclr,zmaruo/coreclr,perfectphase/coreclr,fernando-rodriguez/coreclr,dkorolev/coreclr,bjjones/coreclr,apanda/coreclr,gkhanna79/coreclr,chuck-mitchell/coreclr,KrzysztofCwalina/coreclr,Godin/coreclr,matthubin/coreclr,gkhanna79/coreclr,orthoxerox/coreclr,MCGPPeters/coreclr,sagood/coreclr,dkorolev/coreclr,jamesqo/coreclr,perfectphase/coreclr,matthubin/coreclr,grokys/coreclr,jamesqo/coreclr,hseok-oh/coreclr,perfectphase/coreclr,DickvdBrink/coreclr,chenxizhang/coreclr,bitcrazed/coreclr,dasMulli/coreclr,wkchoy74/coreclr,perfectphase/coreclr,dpodder/coreclr,zmaruo/coreclr,swgillespie/coreclr,yeaicc/coreclr,YongseopKim/coreclr,poizan42/coreclr,serenabenny/coreclr,chenxizhang/coreclr,sejongoh/coreclr,jamesqo/coreclr,dkorolev/coreclr,chuck-mitchell/coreclr,mocsy/coreclr,Lucrecious/coreclr,martinwoodward/coreclr,Sridhar-MS/coreclr,schellap/coreclr,OryJuVog/coreclr,ramarag/coreclr,naamunds/coreclr,matthubin/coreclr,xtypebee/coreclr,benpye/coreclr,mokchhya/coreclr,JonHanna/coreclr,mskvortsov/coreclr,chuck-mitchell/coreclr,Alcaro/coreclr,krixalis/coreclr,JonHanna/coreclr,wkchoy74/coreclr,vinnyrom/coreclr,OryJuVog/coreclr,chaos7theory/coreclr,mskvortsov/coreclr,Godin/coreclr,LLITCHEV/coreclr,wtgodbe/coreclr,DasAllFolks/coreclr,SpotLabsNET/coreclr,andschwa/coreclr,DasAllFolks/coreclr,jhendrixMSFT/coreclr,qiudesong/coreclr,swgillespie/coreclr,GuilhermeSa/coreclr,chrishaly/coreclr,xtypebee/coreclr,DasAllFolks/coreclr,poizan42/coreclr,neurospeech/coreclr,taylorjonl/coreclr,benpye/coreclr,gitchomik/coreclr,blackdwarf/coreclr,qiudesong/coreclr,mokchhya/coreclr,xoofx/coreclr,schellap/coreclr,jhendrixMSFT/coreclr,bartdesmet/coreclr,fernando-rodriguez/coreclr,zmaruo/coreclr,ramarag/coreclr,pgavlin/coreclr,lzcj4/coreclr,JonHanna/coreclr,xoofx/coreclr,martinwoodward/coreclr,ganeshran/coreclr,mmitche/coreclr,yeaicc/coreclr,ericeil/coreclr,chrishaly/coreclr,dpodder/coreclr,hanu412/coreclr,schellap/coreclr,bjjones/coreclr,hseok-oh/coreclr,manu-silicon/coreclr,ruben-ayrapetyan/coreclr,Godin/coreclr,parjong/coreclr,MCGPPeters/coreclr,MCGPPeters/coreclr,xoofx/coreclr,zmaruo/coreclr,krytarowski/coreclr,ytechie/coreclr,chenxizhang/coreclr,botaberg/coreclr,fieryorc/coreclr,lzcj4/coreclr,orthoxerox/coreclr,Dmitry-Me/coreclr,fernando-rodriguez/coreclr,gitchomik/coreclr,shahid-pk/coreclr,tijoytom/coreclr,wateret/coreclr,tijoytom/coreclr,shana/coreclr,misterzik/coreclr,parjong/coreclr,wateret/coreclr,hanu412/coreclr,DasAllFolks/coreclr,stormleoxia/coreclr,fieryorc/coreclr,yeaicc/coreclr,shana/coreclr,krixalis/coreclr,Sridhar-MS/coreclr,poizan42/coreclr,shahid-pk/coreclr,GuilhermeSa/coreclr,AlfredoMS/coreclr,James-Ko/coreclr,yizhang82/coreclr,Sridhar-MS/coreclr,bartonjs/coreclr,martinwoodward/coreclr,cmckinsey/coreclr,cydhaselton/coreclr,sergey-raevskiy/coreclr,matthubin/coreclr,orthoxerox/coreclr,benpye/coreclr,parjong/coreclr,neurospeech/coreclr,MCGPPeters/coreclr,iamjasonp/coreclr,hanu412/coreclr,kyulee1/coreclr,shana/coreclr,jhendrixMSFT/coreclr,swgillespie/coreclr,SpotLabsNET/coreclr,wtgodbe/coreclr,ktos/coreclr,wkchoy74/coreclr,krytarowski/coreclr,sergey-raevskiy/coreclr,Sridhar-MS/coreclr,josteink/coreclr,cydhaselton/coreclr,cydhaselton/coreclr,jhendrixMSFT/coreclr,Djuffin/coreclr,wkchoy74/coreclr,qiudesong/coreclr,krixalis/coreclr,ZhichengZhu/coreclr,AlfredoMS/coreclr,yizhang82/coreclr,taylorjonl/coreclr,sagood/coreclr,ericeil/coreclr,sjsinju/coreclr,orthoxerox/coreclr,DickvdBrink/coreclr,sperling/coreclr,xtypebee/coreclr,alexperovich/coreclr,Samana/coreclr,jamesqo/coreclr,sjsinju/coreclr,chrishaly/coreclr,poizan42/coreclr,ganeshran/coreclr,mocsy/coreclr,xoofx/coreclr,JosephTremoulet/coreclr,cshung/coreclr,YongseopKim/coreclr,sergey-raevskiy/coreclr,martinwoodward/coreclr,bitcrazed/coreclr,shana/coreclr,pgavlin/coreclr,AlexGhiondea/coreclr,dkorolev/coreclr,ZhichengZhu/coreclr,spoiledsport/coreclr,dkorolev/coreclr,cmckinsey/coreclr,yizhang82/coreclr,alexperovich/coreclr,sagood/coreclr,AlexGhiondea/coreclr,josteink/coreclr,ruben-ayrapetyan/coreclr,Dmitry-Me/coreclr,alexperovich/coreclr,krk/coreclr,hseok-oh/coreclr,vinnyrom/coreclr,josteink/coreclr,libengu/coreclr,LLITCHEV/coreclr,naamunds/coreclr,KrzysztofCwalina/coreclr,SlavaRa/coreclr,gkhanna79/coreclr,mokchhya/coreclr,iamjasonp/coreclr,botaberg/coreclr,manu-silicon/coreclr,LLITCHEV/coreclr,botaberg/coreclr,shana/coreclr,josteink/coreclr,qiudesong/coreclr,Samana/coreclr,tijoytom/coreclr,ragmani/coreclr,AlfredoMS/coreclr,fieryorc/coreclr,sjsinju/coreclr,shahid-pk/coreclr,DickvdBrink/coreclr,ytechie/coreclr,andschwa/coreclr,grokys/coreclr,fffej/coreclr,SlavaRa/coreclr,orthoxerox/coreclr,sjsinju/coreclr,sperling/coreclr,Alcaro/coreclr,dasMulli/coreclr,fffej/coreclr,chaos7theory/coreclr,zmaruo/coreclr,krixalis/coreclr,Alcaro/coreclr,apanda/coreclr,Djuffin/coreclr,krytarowski/coreclr,ktos/coreclr,andschwa/coreclr,chuck-mitchell/coreclr,spoiledsport/coreclr,xoofx/coreclr,taylorjonl/coreclr,chrishaly/coreclr,neurospeech/coreclr,mocsy/coreclr,xoofx/coreclr,SpotLabsNET/coreclr,sergey-raevskiy/coreclr,fernando-rodriguez/coreclr,Alcaro/coreclr,jamesqo/coreclr,pgavlin/coreclr,stormleoxia/coreclr,benpye/coreclr,wtgodbe/coreclr,andschwa/coreclr,bartonjs/coreclr,Lucrecious/coreclr,libengu/coreclr,mokchhya/coreclr,neurospeech/coreclr,krk/coreclr,ganeshran/coreclr,sperling/coreclr,cmckinsey/coreclr,AlfredoMS/coreclr,benpye/coreclr,swgillespie/coreclr,kyulee1/coreclr,Samana/coreclr,Samana/coreclr,bitcrazed/coreclr,ruben-ayrapetyan/coreclr,GuilhermeSa/coreclr,mokchhya/coreclr,sperling/coreclr,grokys/coreclr,wateret/coreclr,sergey-raevskiy/coreclr,david-mitchell/coreclr,pgavlin/coreclr,cmckinsey/coreclr,dpodder/coreclr,manu-silicon/coreclr,chaos7theory/coreclr,GuilhermeSa/coreclr,ruben-ayrapetyan/coreclr,Lucrecious/coreclr,wtgodbe/coreclr,martinwoodward/coreclr,chaos7theory/coreclr,lzcj4/coreclr,hanu412/coreclr,roncain/coreclr,jakesays/coreclr,JonHanna/coreclr,benpye/coreclr,ZhichengZhu/coreclr,andschwa/coreclr,blackdwarf/coreclr,martinwoodward/coreclr,KrzysztofCwalina/coreclr,KrzysztofCwalina/coreclr,ramarag/coreclr,vinnyrom/coreclr,sperling/coreclr,vinnyrom/coreclr,ruben-ayrapetyan/coreclr,ytechie/coreclr,stormleoxia/coreclr,AlfredoMS/coreclr,botaberg/coreclr,gitchomik/coreclr,jamesqo/coreclr,Lucrecious/coreclr,stormleoxia/coreclr,naamunds/coreclr,Samana/coreclr,krytarowski/coreclr,Alcaro/coreclr,bartdesmet/coreclr,wkchoy74/coreclr,alexperovich/coreclr,vinnyrom/coreclr,wateret/coreclr,yeaicc/coreclr,mmitche/coreclr,Godin/coreclr,SlavaRa/coreclr,gitchomik/coreclr,iamjasonp/coreclr,dpodder/coreclr,taylorjonl/coreclr,naamunds/coreclr,yeaicc/coreclr,KrzysztofCwalina/coreclr,geertdoornbos/coreclr,dasMulli/coreclr,ericeil/coreclr,LLITCHEV/coreclr,russellhadley/coreclr,dasMulli/coreclr,xtypebee/coreclr,roncain/coreclr,richardlford/coreclr,AlexGhiondea/coreclr,richardlford/coreclr,wateret/coreclr,apanda/coreclr,mocsy/coreclr,rartemev/coreclr,James-Ko/coreclr,schellap/coreclr,mskvortsov/coreclr,pgavlin/coreclr,bartdesmet/coreclr,ramarag/coreclr,poizan42/coreclr,chenxizhang/coreclr,fieryorc/coreclr,krk/coreclr,jhendrixMSFT/coreclr,fieryorc/coreclr,Dmitry-Me/coreclr,roncain/coreclr,parjong/coreclr,Djuffin/coreclr,hseok-oh/coreclr,dpodder/coreclr,MCGPPeters/coreclr,shahid-pk/coreclr,YongseopKim/coreclr,krixalis/coreclr,jakesays/coreclr,OryJuVog/coreclr,fernando-rodriguez/coreclr,grokys/coreclr,chuck-mitchell/coreclr,Dmitry-Me/coreclr,kyulee1/coreclr,OryJuVog/coreclr,ericeil/coreclr,JosephTremoulet/coreclr,sjsinju/coreclr,chuck-mitchell/coreclr,geertdoornbos/coreclr,mmitche/coreclr,YongseopKim/coreclr,cshung/coreclr,OryJuVog/coreclr,manu-silicon/coreclr,ragmani/coreclr,xtypebee/coreclr,blackdwarf/coreclr,wkchoy74/coreclr,ganeshran/coreclr,blackdwarf/coreclr,bitcrazed/coreclr,manu-silicon/coreclr,shahid-pk/coreclr,vinnyrom/coreclr,andschwa/coreclr,mokchhya/coreclr,James-Ko/coreclr,cshung/coreclr,jakesays/coreclr,ganeshran/coreclr,KrzysztofCwalina/coreclr,Lucrecious/coreclr,roncain/coreclr,schellap/coreclr,chrishaly/coreclr,ktos/coreclr,MCGPPeters/coreclr,naamunds/coreclr,jakesays/coreclr,ZhichengZhu/coreclr,gitchomik/coreclr,kyulee1/coreclr,perfectphase/coreclr,Sridhar-MS/coreclr,hanu412/coreclr,Lucrecious/coreclr,chaos7theory/coreclr,blackdwarf/coreclr,Dmitry-Me/coreclr,naamunds/coreclr,ytechie/coreclr,lzcj4/coreclr,apanda/coreclr,richardlford/coreclr,ktos/coreclr,Godin/coreclr,cydhaselton/coreclr,ragmani/coreclr,bartonjs/coreclr,bjjones/coreclr,cshung/coreclr,fffej/coreclr,botaberg/coreclr,botaberg/coreclr,jakesays/coreclr,LLITCHEV/coreclr,benpye/coreclr,JosephTremoulet/coreclr,roncain/coreclr,xtypebee/coreclr,david-mitchell/coreclr,ericeil/coreclr,Godin/coreclr,gkhanna79/coreclr,krytarowski/coreclr,alexperovich/coreclr,david-mitchell/coreclr,sejongoh/coreclr,Godin/coreclr,DasAllFolks/coreclr,sjsinju/coreclr,mskvortsov/coreclr,LLITCHEV/coreclr,bitcrazed/coreclr,bitcrazed/coreclr,yizhang82/coreclr,serenabenny/coreclr,mocsy/coreclr,sejongoh/coreclr,rartemev/coreclr,cmckinsey/coreclr,gitchomik/coreclr,Dmitry-Me/coreclr,fffej/coreclr,richardlford/coreclr,roncain/coreclr,chrishaly/coreclr,russellhadley/coreclr,spoiledsport/coreclr,poizan42/coreclr,tijoytom/coreclr,dkorolev/coreclr,grokys/coreclr,alexperovich/coreclr,fffej/coreclr,yizhang82/coreclr,Sridhar-MS/coreclr,serenabenny/coreclr,Samana/coreclr,bjjones/coreclr,cmckinsey/coreclr,wtgodbe/coreclr,misterzik/coreclr,swgillespie/coreclr,ZhichengZhu/coreclr,wateret/coreclr,sergey-raevskiy/coreclr,rartemev/coreclr,bartdesmet/coreclr,parjong/coreclr,russellhadley/coreclr,kyulee1/coreclr,James-Ko/coreclr,krytarowski/coreclr,manu-silicon/coreclr,bitcrazed/coreclr,SlavaRa/coreclr,James-Ko/coreclr,iamjasonp/coreclr,bartdesmet/coreclr,ytechie/coreclr,hseok-oh/coreclr,bjjones/coreclr,serenabenny/coreclr,Dmitry-Me/coreclr,chuck-mitchell/coreclr,jakesays/coreclr,neurospeech/coreclr,krk/coreclr,wtgodbe/coreclr,rartemev/coreclr,sejongoh/coreclr,cmckinsey/coreclr,AlexGhiondea/coreclr,spoiledsport/coreclr,cshung/coreclr,david-mitchell/coreclr,geertdoornbos/coreclr,JosephTremoulet/coreclr,david-mitchell/coreclr,LLITCHEV/coreclr,sagood/coreclr,misterzik/coreclr,Djuffin/coreclr,Djuffin/coreclr,qiudesong/coreclr,JosephTremoulet/coreclr,KrzysztofCwalina/coreclr,geertdoornbos/coreclr,libengu/coreclr,DasAllFolks/coreclr,chenxizhang/coreclr,misterzik/coreclr,cydhaselton/coreclr,dasMulli/coreclr,bjjones/coreclr,zmaruo/coreclr,apanda/coreclr,JonHanna/coreclr,andschwa/coreclr,ktos/coreclr,OryJuVog/coreclr,matthubin/coreclr,SpotLabsNET/coreclr,libengu/coreclr,martinwoodward/coreclr,sagood/coreclr,vinnyrom/coreclr,fernando-rodriguez/coreclr,ktos/coreclr,mmitche/coreclr,apanda/coreclr,grokys/coreclr,ktos/coreclr,serenabenny/coreclr,Alcaro/coreclr,geertdoornbos/coreclr,josteink/coreclr,ganeshran/coreclr,AlfredoMS/coreclr,YongseopKim/coreclr,ramarag/coreclr,ragmani/coreclr,josteink/coreclr,GuilhermeSa/coreclr,YongseopKim/coreclr,fffej/coreclr,JosephTremoulet/coreclr,rartemev/coreclr,chenxizhang/coreclr,ZhichengZhu/coreclr,JonHanna/coreclr,lzcj4/coreclr