auto merge of #16216 : omasanori/rust/nfkc, r=brson
auto merge of #16216 : omasanori/rust/nfkc, r=brson

The reference manual said that code is interpreted as UTF-8 text and a implementation will normalize it to NFKC. However, rustc doesn't do any normalization now.

We may want to do any normalization for symbols, but normalizing whole text seems harmful because doing so loses some sort of information even if we choose a non-K variant of normalization.

I'd suggest removing "normalized to Unicode normalization form NFKC" phrase for the present so that the manual represents the current state properly. When we address the problem (with a RFC?), then the manual should be updated.

Closes #12388.

Reference: https://github.com/rust-lang/rust/issues/2253

seanrivera/rust,P1start/rust,pshc/rust,AerialX/rust-rt-minimal,barosl/rust,miniupnp/rust,quornian/rust,KokaKiwi/rust,ktossell/rust,hauleth/rust,zaeleus/rust,nwin/rust,XMPPwocky/rust,ktossell/rust,miniupnp/rust,pshc/rust,aidancully/rust,barosl/rust,pshc/rust,GBGamer/rust,l0kod/rust,victorvde/rust,rprichard/rust,philyoon/rust,sae-bom/rust,seanrivera/rust,robertg/rust,gifnksm/rust,seanrivera/rust,sae-bom/rust,KokaKiwi/rust,reem/rust,pelmers/rust,zubron/rust,gifnksm/rust,GBGamer/rust,mvdnes/rust,0x73/rust,l0kod/rust,cllns/rust,nwin/rust,untitaker/rust,AerialX/rust-rt-minimal,miniupnp/rust,zachwick/rust,mihneadb/rust,kimroen/rust,ebfull/rust,andars/rust,kwantam/rust,erickt/rust,P1start/rust,carols10cents/rust,pelmers/rust,erickt/rust,aepsil0n/rust,ebfull/rust,ruud-v-a/rust,nham/rust,untitaker/rust,quornian/rust,zaeleus/rust,emk/rust,graydon/rust,seanrivera/rust,zubron/rust,seanrivera/rust,zachwick/rust,pshc/rust,erickt/rust,TheNeikos/rust,victorvde/rust,richo/rust,ruud-v-a/rust,bombless/rust,GBGamer/rust,hauleth/rust,jashank/rust,mihneadb/rust,richo/rust,jroesch/rust,robertg/rust,rohitjoshi/rust,bombless/rust,omasanori/rust,mahkoh/rust,XMPPwocky/rust,jroesch/rust,erickt/rust,pelmers/rust,emk/rust,rprichard/rust,graydon/rust,mvdnes/rust,philyoon/rust,l0kod/rust,P1start/rust,barosl/rust,aepsil0n/rust,ejjeong/rust,mvdnes/rust,ktossell/rust,andars/rust,mvdnes/rust,vhbit/rust,GBGamer/rust,0x73/rust,ruud-v-a/rust,P1start/rust,cllns/rust,XMPPwocky/rust,sae-bom/rust,P1start/rust,mihneadb/rust,mdinger/rust,reem/rust,philyoon/rust,l0kod/rust,nwin/rust,0x73/rust,graydon/rust,andars/rust,mahkoh/rust,emk/rust,aneeshusa/rust,emk/rust,robertg/rust,jashank/rust,ejjeong/rust,robertg/rust,victorvde/rust,jroesch/rust,sae-bom/rust,GBGamer/rust,vhbit/rust,mihneadb/rust,aneeshusa/rust,reem/rust,carols10cents/rust,pshc/rust,aepsil0n/rust,bombless/rust,dwillmer/rust,miniupnp/rust,mihneadb/rust,zubron/rust,dwillmer/rust,GBGamer/rust,P1start/rust,gifnksm/rust,rprichard/rust,nwin/rust,reem/rust,omasanori/rust,rohitjoshi/rust,nham/rust,bombless/rust,aidancully/rust,victorvde/rust,ejjeong/rust,andars/rust,dinfuehr/rust,cllns/rust,XMPPwocky/rust,nwin/rust,krzysz00/rust,quornian/rust,aidancully/rust,cllns/rust,richo/rust,omasanori/rust,kwantam/rust,nwin/rust,zaeleus/rust,philyoon/rust,ebfull/rust,zubron/rust,untitaker/rust,reem/rust,bombless/rust,rprichard/rust,kimroen/rust,gifnksm/rust,graydon/rust,aepsil0n/rust,graydon/rust,emk/rust,KokaKiwi/rust,carols10cents/rust,ejjeong/rust,avdi/rust,seanrivera/rust,jashank/rust,jashank/rust,defuz/rust,richo/rust,krzysz00/rust,mdinger/rust,dwillmer/rust,dwillmer/rust,jashank/rust,miniupnp/rust,dinfuehr/rust,TheNeikos/rust,jbclements/rust,hauleth/rust,emk/rust,miniupnp/rust,mahkoh/rust,vhbit/rust,jbclements/rust,pshc/rust,avdi/rust,AerialX/rust,ktossell/rust,kwantam/rust,dinfuehr/rust,carols10cents/rust,jroesch/rust,0x73/rust,erickt/rust,dwillmer/rust,mahkoh/rust,mvdnes/rust,defuz/rust,avdi/rust,kwantam/rust,barosl/rust,l0kod/rust,ktossell/rust,quornian/rust,kimroen/rust,gifnksm/rust,jashank/rust,krzysz00/rust,zubron/rust,aidancully/rust,quornian/rust,mdinger/rust,TheNeikos/rust,sae-bom/rust,barosl/rust,emk/rust,dwillmer/rust,zaeleus/rust,gifnksm/rust,krzysz00/rust,avdi/rust,mahkoh/rust,pshc/rust,ebfull/rust,mdinger/rust,mahkoh/rust,nham/rust,robertg/rust,AerialX/rust,dinfuehr/rust,ejjeong/rust,jroesch/rust,hauleth/rust,ejjeong/rust,miniupnp/rust,ebfull/rust,kwantam/rust,aidancully/rust,jbclements/rust,vhbit/rust,zachwick/rust,aepsil0n/rust,TheNeikos/rust,rohitjoshi/rust,jroesch/rust,cllns/rust,barosl/rust,richo/rust,GBGamer/rust,jroesch/rust,defuz/rust,rohitjoshi/rust,dwillmer/rust,kimroen/rust,l0kod/rust,sae-bom/rust,avdi/rust,nwin/rust,ruud-v-a/rust,vhbit/rust,kimroen/rust,0x73/rust,AerialX/rust-rt-minimal,carols10cents/rust,andars/rust,rohitjoshi/rust,jashank/rust,kimroen/rust,dinfuehr/rust,ruud-v-a/rust,jbclements/rust,vhbit/rust,KokaKiwi/rust,hauleth/rust,aepsil0n/rust,vhbit/rust,jbclements/rust,kimroen/rust,barosl/rust,GBGamer/rust,aidancully/rust,rohitjoshi/rust,0x73/rust,AerialX/rust-rt-minimal,zaeleus/rust,victorvde/rust,avdi/rust,dwillmer/rust,jbclements/rust,erickt/rust,ruud-v-a/rust,kwantam/rust,mihneadb/rust,dinfuehr/rust,aneeshusa/rust,P1start/rust,mvdnes/rust,graydon/rust,carols10cents/rust,XMPPwocky/rust,miniupnp/rust,defuz/rust,vhbit/rust,untitaker/rust,pshc/rust,omasanori/rust,jashank/rust,victorvde/rust,XMPPwocky/rust,jbclements/rust,aneeshusa/rust,richo/rust,untitaker/rust,hauleth/rust,zaeleus/rust,philyoon/rust,robertg/rust,zachwick/rust,AerialX/rust,defuz/rust,ktossell/rust,andars/rust,0x73/rust,cllns/rust,pelmers/rust,KokaKiwi/rust,jroesch/rust,krzysz00/rust,jbclements/rust,quornian/rust,AerialX/rust,bombless/rust-docs-chinese,rprichard/rust,erickt/rust,omasanori/rust,defuz/rust,zubron/rust,omasanori/rust,jbclements/rust,aneeshusa/rust,TheNeikos/rust,aneeshusa/rust,l0kod/rust,krzysz00/rust,l0kod/rust,nwin/rust,philyoon/rust,AerialX/rust-rt-minimal,reem/rust,AerialX/rust,AerialX/ru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