Add types for execSync, execFileSync, spawnSync
Add types for execSync, execFileSync, spawnSync

The types added in this commit were designed based on the definitions of
the relevant functions
(here)[https://nodejs.org/api/child_process.html#child_process_synchronous_process_creation]

An attempt was made to follow the conventions found in lib/node.js, but
there wasn't a precedent for return objects hence the name spawnRet.

shiftcars/flow,nmote/flow,nmote/flow,jamesgpearce/flow,JeckoHeroOrg/flow,MichaelDeBoey/flow,shiftcars/flow,nmote/flow,jamesgpearce/flow,cesarandreu/flow,MichaelDeBoey/flow,jeffutter/flow,KevinTCoughlin/flow,Fresheyeball/flow,CJstar/flow,JohnyDays/flow,Drooids/flow,mroch/flow,fletcherw/flow,rafaelstz/flow,fletcherw/flow,Eyyub/flow,MichaelDeBoey/flow,jdelStrother/flow,AgentME/flow,AprilArcus/flow,gabro/flow,Fresheyeball/flow,popham/flow,popham/flow,jeffutter/flow,rafaelstz/flow,davidmason/flow,jdelStrother/flow,d14b3l/flow,graue/flow,chenglou/flow,claudiopro/flow,gabelevi/flow,shiftcars/flow,samwgoldman/flow,Drooids/flow,asivitz/flow,AgentME/flow,davidmason/flow,JonathanUsername/flow,gabelevi/flow,gabelevi/flow,mroch/flow,jamesgpearce/flow,jgrund/flow,paulshen/flow,graue/flow,graue/flow,TiddoLangerak/flow,gabelevi/flow,chenglou/flow,CJstar/flow,jgrund/flow,jdelStrother/flow,jgrund/flow,chenglou/flow,facebook/flow,ylu1317/flow,danvk/flow,gabelevi/flow,facebook/flow,JohnyDays/flow,lyip1992/flow,gabelevi/flow,nmote/flow,danvk/flow,JeckoHeroOrg/flow,AprilArcus/flow,ianobermiller/flow,gabro/flow,lyip1992/flow,mcanthony/flow-type,asivitz/flow,YelaSeamless/flow,claudiopro/flow,matklad/flow,jamesgpearce/flow,shiftcars/flow,paulshen/flow,mroch/flow,rafaelstz/flow,Eyyub/flow,ForbesLindesay/flow,gabelevi/flow,TiddoLangerak/flow,dv/flow,jeffmo/flow,darioajr/flow,fletcherw/flow,Jericho25/flow,Drooids/flow,YelaSeamless/flow,JeckoHeroOrg/flow,JeckoHeroOrg/flow,ForbesLindesay/flow,gabro/flow,mroch/flow,AprilArcus/flow,asivitz/flow,cesarandreu/flow,davidmason/flow,samwgoldman/flow,graue/flow,lyip1992/flow,facebook/flow,darioajr/flow,KevinTCoughlin/flow,ForbesLindesay/flow,mcanthony/flow-type,chenglou/flow,popham/flow,d14b3l/flow,Fresheyeball/flow,gabro/flow,jeffmo/flow,claudiopro/flow,JohnyDays/flow,nmote/flow,claudiopro/flow,TiddoLangerak/flow,danvk/flow,jdelStrother/flow,mroch/flow,jgrund/flow,facebook/flow,Eyyub/flow,asivitz/flow,samwgoldman/flow,jdelStrother/flow,Eyyub/flow,ForbesLindesay/flow,graue/flow,rafaelstz/flow,Wanderfalke/flow,Jericho25/flow,OCamlPro/flow,darioajr/flow,ForbesLindesay/flow,fletcherw/flow,popham/flow,dv/flow,d14b3l/flow,nmote/flow,ylu1317/flow,CJstar/flow,OCamlPro/flow,davidmason/flow,siddhartharay007/flow,runn1ng/flow,Jericho25/flow,shiftcars/flow,jamesgpearce/flow,facebook/flow,danvk/flow,runn1ng/flow,chenglou/flow,runn1ng/flow,ylu1317/flow,JonathanUsername/flow,AprilArcus/flow,facebook/flow,siddhartharay007/flow,jdelStrother/flow,shiftcars/flow,OCamlPro/flow,CJstar/flow,fletcherw/flow,jeffmo/flow,MichaelDeBoey/flow,runn1ng/flow,popham/flow,facebook/flow,jgrund/flow,mroch/flow,davidmason/flow,jeffmo/flow,jeffmo/flow,jgrund/flow,OCamlPro/flow,TiddoLangerak/flow,samwgoldman/flow,rafaelstz/flow,graue/flow,MichaelDeBoey/flow,samwgoldman/flow,dv/flow,nmote/flow,claudiopro/flow,mroch/flow,ForbesLindesay/flow,JonathanUsername/flow,chenglou/flow,lyip1992/flow,fletcherw/flow,d14b3l/flow,Drooids/flow,KevinTCoughlin/flow,AprilArcus/flow,mcanthony/flow-type,Wanderfalke/flow,ianobermiller/flow,matklad/flow,dv/flow,siddhartharay007/flow,TiddoLangerak/flow,popham/flow,ylu1317/flow,JonathanUsername/flow,d14b3l/flow,matklad/flow,jamesgpearce/flow,YelaSeamless/flow,jamesgpearce/flow,matklad/flow,gabro/flow,popham/flow,jeffutter/flow,ianobermiller/flow,JonathanUsername/flow,samwgoldman/flow,AgentME/flow,AprilArcus/flow,Fresheyeball/flow,paulshen/flow,darioajr/flow,JonathanUsername/flow,matklad/flow,siddhartharay007/flow,JeckoHeroOrg/flow,samwgoldman/flow,mcanthony/flow-type,cesarandreu/flow,Wanderfalke/flow,cesarandreu/flow,paulshen/flow,jeffmo/flow,KevinTCoughlin/flow,d14b3l/flow,JohnyDays/flow,JonathanUsername/flow,YelaSeamless/flow,Wanderfalke/flow,YelaSeamless/flow,ianobermiller/flow,AgentME/flow,AgentME/flow,ylu1317/flow,gabro/flow,jeffutter/flow