rustdoc: Render default methods for impls as well
rustdoc: Render default methods for impls as well

This does not work for cross-crate implementations of traits. Cross-crate
implementations are a separate issue that should be addressed separately.
Basically when an implementation of an external trait is detected, the trait
would have to be loaded at that time (or possibly sooner...). Rustdoc currently
doesn't have the proper infrastructure for adding this.

Closes #9985
cc #9999

fabricedesre/rust,nwin/rust,andars/rust,miniupnp/rust,avdi/rust,hauleth/rust,Ryman/rust,jbclements/rust,ejjeong/rust,pczarn/rust,l0kod/rust,omasanori/rust,defuz/rust,barosl/rust,quornian/rust,zubron/rust,fabricedesre/rust,mitsuhiko/rust,andars/rust,fabricedesre/rust,zaeleus/rust,aneeshusa/rust,KokaKiwi/rust,retep998/rand,servo/rust,nwin/rust,kimroen/rust,pczarn/rust,kwantam/rust,jbclements/rust,zachwick/rust,Ryman/rust,aneeshusa/rust,aepsil0n/rust,jashank/rust,mdinger/rust,avdi/rust,mahkoh/rust,arthurprs/rand,KokaKiwi/rust,zubron/rust,P1start/rust,mvdnes/rust,dwillmer/rust,ejjeong/rust,kimroen/rust,michaelballantyne/rust-gpu,erickt/rust,nham/rust,zubron/rust,michaelballantyne/rust-gpu,andars/rust,fabricedesre/rust,SiegeLord/rust,ktossell/rust,omasanori/rust,nham/rust,jashank/rust,vhbit/rust,mahkoh/rust,carols10cents/rust,pczarn/rust,mitsuhiko/rust,aepsil0n/rust,ebfull/rust,0x73/rust,graydon/rust,GBGamer/rust,nham/rust,ebfull/rust,bombless/rust,AerialX/rust-rt-minimal,untitaker/rust,pythonesque/rust,kwantam/rust,aidancully/rust,bhickey/rand,graydon/rust,kwantam/rust,nham/rust,l0kod/rust,l0kod/rust,ejjeong/rust,aepsil0n/rust,pelmers/rust,jbclements/rust,XMPPwocky/rust,philyoon/rust,jbclements/rust,zachwick/rust,pshc/rust,hauleth/rust,dwillmer/rust,emk/rust,andars/rust,shepmaster/rand,miniupnp/rust,miniupnp/rust,pelmers/rust,SiegeLord/rust,emk/rust,omasanori/rust,philyoon/rust,barosl/rust,l0kod/rust,XMPPwocky/rust,quornian/rust,zubron/rust,hauleth/rust,Ryman/rust,sae-bom/rust,gifnksm/rust,l0kod/rust,GBGamer/rust,philyoon/rust,avdi/rust,zachwick/rust,gifnksm/rust,richo/rust,AerialX/rust,krzysz00/rust,pshc/rust,servo/rust,TheNeikos/rust,omasanori/rust,jashank/rust,fabricedesre/rust,AerialX/rust,krzysz00/rust,michaelballantyne/rust-gpu,vhbit/rust,pshc/rust,ebfull/rust,P1start/rust,aturon/rust,philyoon/rust,erickt/rust,erickt/rust,Ryman/rust,victorvde/rust,michaelballantyne/rust-gpu,0x73/rust,nham/rust,jbclements/rust,AerialX/rust,AerialX/rust-rt-minimal,sae-bom/rust,huonw/rand,XMPPwocky/rust,bombless/rust,aepsil0n/rust,philyoon/rust,pczarn/rust,quornian/rust,GBGamer/rust,nwin/rust,defuz/rust,vhbit/rust,robertg/rust,vhbit/rust,jroesch/rust,aturon/rust,dinfuehr/rust,reem/rust,avdi/rust,dinfuehr/rust,SiegeLord/rust,bombless/rust,emk/rust,stepancheg/rust-ide-rust,stepancheg/rust-ide-rust,seanrivera/rust,rohitjoshi/rust,TheNeikos/rust,vhbit/rust,Ryman/rust,untitaker/rust,ktossell/rust,servo/rust,KokaKiwi/rust,mvdnes/rust,TheNeikos/rust,kimroen/rust,aidancully/rust,cllns/rust,ejjeong/rust,pythonesque/rust,zaeleus/rust,servo/rust,pelmers/rust,GBGamer/rust,AerialX/rust,l0kod/rust,miniupnp/rust,bluss/rand,kimroen/rust,SiegeLord/rust,robertg/rust,ebfull/rust,mvdnes/rust,zaeleus/rust,rprichard/rust,barosl/rust,krzysz00/rust,hauleth/rust,bombless/rust,mvdnes/rust,GrahamDennis/rand,pczarn/rust,rprichard/rust,aneeshusa/rust,carols10cents/rust,graydon/rust,rohitjoshi/rust,miniupnp/rust,XMPPwocky/rust,erickt/rust,omasanori/rust,rohitjoshi/rust,reem/rust,aturon/rust,pythonesque/rust,miniupnp/rust,mitsuhiko/rust,quornian/rust,reem/rust,Ryman/rust,zachwick/rust,GBGamer/rust,dinfuehr/rust,richo/rust,achanda/rand,TheNeikos/rust,dwillmer/rust,aepsil0n/rust,0x73/rust,carols10cents/rust,ktossell/rust,cllns/rust,barosl/rust,SiegeLord/rust,pshc/rust,GBGamer/rust,pythonesque/rust,mdinger/rust,rohitjoshi/rust,untitaker/rust,P1start/rust,ebfull/rand,pelmers/rust,ktossell/rust,carols10cents/rust,untitaker/rust,ejjeong/rust,miniupnp/rust,aneeshusa/rust,ruud-v-a/rust,zaeleus/rust,XMPPwocky/rust,defuz/rust,gifnksm/rust,jroesch/rust,zubron/rust,ruud-v-a/rust,seanrivera/rust,seanrivera/rust,mihneadb/rust,graydon/rust,vhbit/rust,dwillmer/rust,aidancully/rust,servo/rust,aepsil0n/rust,cllns/rust,philyoon/rust,fabricedesre/rust,nham/rust,ruud-v-a/rust,rohitjoshi/rust,carols10cents/rust,gifnksm/rust,pshc/rust,reem/rust,vhbit/rust,robertg/rust,seanrivera/rust,mihneadb/rust,dwillmer/rust,gifnksm/rust,TheNeikos/rust,zachwick/rust,AerialX/rust,barosl/rust,GBGamer/rust,richo/rust,kwantam/rust,robertg/rust,rprichard/rust,rohitjoshi/rust,pythonesque/rust,defuz/rust,emk/rust,kimroen/rust,P1start/rust,stepancheg/rust-ide-rust,untitaker/rust,michaelballantyne/rust-gpu,sae-bom/rust,AerialX/rust-rt-minimal,graydon/rust,krzysz00/rust,victorvde/rust,mihneadb/rust,zubron/rust,cllns/rust,mihneadb/rust,mitsuhiko/rust,aturon/rust,mdinger/rust,aidancully/rust,KokaKiwi/rust,rprichard/rust,quornian/rust,jroesch/rust,emk/rust,SiegeLord/rust,barosl/rust,defuz/rust,robertg/rust,zubron/rust,carols10cents/rust,jashank/rust,erickt/rust,dwillmer/rust,kimroen/rust,aneeshusa/rust,bombless/rust-docs-chinese,P1start/rust,krzysz00/rust,cllns/rust,AerialX/rust-rt-minimal,l0kod/rust,pczarn/rust,ktossell/rust,pshc/rust,pczarn/rust,mvdnes/rust,zubron/rust,dinfuehr/rust,hauleth/rust,mahkoh/rust,richo/rust,AerialX/rust-rt-minimal,stepancheg/rust-ide-rust,mitsuhiko/rust,andars/rust,avdi/rust,hauleth/rust,kimroen/rust,aneeshusa/rust,servo/rust,vhbit/rust,zaeleus/rust,jbclements/rust,jroesch/r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