rollup merge of #23652: alexcrichton/stabilize-hasher-finish
rollup merge of #23652: alexcrichton/stabilize-hasher-finish

This commit enables writing a stable implementation of the `Hasher` trait as
well as actually calculating the hash of a vlaue in a stable fashion. The
signature is stabilized as-is.

ruud-v-a/rust,aepsil0n/rust,pelmers/rust,mvdnes/rust,graydon/rust,andars/rust,graydon/rust,andars/rust,jashank/rust,mihneadb/rust,pshc/rust,robertg/rust,aepsil0n/rust,ebfull/rust,aidancully/rust,ejjeong/rust,zaeleus/rust,ebfull/rust,graydon/rust,omasanori/rust,carols10cents/rust,dwillmer/rust,dwillmer/rust,cllns/rust,TheNeikos/rust,aneeshusa/rust,l0kod/rust,vhbit/rust,mihneadb/rust,zaeleus/rust,mihneadb/rust,nwin/rust,robertg/rust,avdi/rust,ebfull/rust,avdi/rust,krzysz00/rust,reem/rust,ejjeong/rust,ejjeong/rust,seanrivera/rust,robertg/rust,KokaKiwi/rust,seanrivera/rust,aneeshusa/rust,aepsil0n/rust,dwillmer/rust,graydon/rust,mvdnes/rust,zubron/rust,pelmers/rust,aneeshusa/rust,mihneadb/rust,seanrivera/rust,reem/rust,zubron/rust,cllns/rust,mvdnes/rust,ejjeong/rust,jroesch/rust,ruud-v-a/rust,zubron/rust,GBGamer/rust,zubron/rust,reem/rust,pelmers/rust,nwin/rust,omasanori/rust,omasanori/rust,vhbit/rust,mihneadb/rust,krzysz00/rust,GBGamer/rust,KokaKiwi/rust,aneeshusa/rust,aepsil0n/rust,sae-bom/rust,rohitjoshi/rust,carols10cents/rust,ejjeong/rust,l0kod/rust,gifnksm/rust,vhbit/rust,TheNeikos/rust,vhbit/rust,pshc/rust,reem/rust,zubron/rust,zubron/rust,GBGamer/rust,philyoon/rust,mvdnes/rust,l0kod/rust,carols10cents/rust,aepsil0n/rust,gifnksm/rust,aepsil0n/rust,seanrivera/rust,pshc/rust,nwin/rust,krzysz00/rust,miniupnp/rust,nwin/rust,robertg/rust,aidancully/rust,mvdnes/rust,avdi/rust,mdinger/rust,zaeleus/rust,jashank/rust,zaeleus/rust,ebfull/rust,pshc/rust,sae-bom/rust,ejjeong/rust,zachwick/rust,victorvde/rust,andars/rust,kwantam/rust,victorvde/rust,zachwick/rust,rohitjoshi/rust,victorvde/rust,KokaKiwi/rust,philyoon/rust,jroesch/rust,XMPPwocky/rust,sae-bom/rust,rohitjoshi/rust,kwantam/rust,TheNeikos/rust,mvdnes/rust,cllns/rust,nwin/rust,aneeshusa/rust,jashank/rust,dwillmer/rust,gifnksm/rust,ruud-v-a/rust,krzysz00/rust,miniupnp/rust,TheNeikos/rust,sae-bom/rust,omasanori/rust,jroesch/rust,l0kod/rust,rohitjoshi/rust,XMPPwocky/rust,avdi/rust,carols10cents/rust,mdinger/rust,kwantam/rust,pshc/rust,andars/rust,krzysz00/rust,miniupnp/rust,vhbit/rust,cllns/rust,l0kod/rust,nwin/rust,pshc/rust,pshc/rust,graydon/rust,jashank/rust,omasanori/rust,philyoon/rust,vhbit/rust,victorvde/rust,jroesch/rust,jroesch/rust,nwin/rust,zachwick/rust,l0kod/rust,seanrivera/rust,dwillmer/rust,seanrivera/rust,GBGamer/rust,miniupnp/rust,pshc/rust,vhbit/rust,dwillmer/rust,miniupnp/rust,jroesch/rust,omasanori/rust,avdi/rust,gifnksm/rust,GBGamer/rust,ebfull/rust,aneeshusa/rust,avdi/rust,robertg/rust,jashank/rust,kwantam/rust,XMPPwocky/rust,miniupnp/rust,mdinger/rust,cllns/rust,zachwick/rust,zachwick/rust,victorvde/rust,mdinger/rust,sae-bom/rust,miniupnp/rust,victorvde/rust,GBGamer/rust,mihneadb/rust,ruud-v-a/rust,zubron/rust,dwillmer/rust,rohitjoshi/rust,philyoon/rust,carols10cents/rust,vhbit/rust,zaeleus/rust,jroesch/rust,sae-bom/rust,KokaKiwi/rust,krzysz00/rust,gifnksm/rust,GBGamer/rust,l0kod/rust,XMPPwocky/rust,XMPPwocky/rust,jroesch/rust,TheNeikos/rust,zaeleus/rust,pelmers/rust,dwillmer/rust,graydon/rust,pelmers/rust,ebfull/rust,mdinger/rust,l0kod/rust,jashank/rust,rohitjoshi/rust,jashank/rust,TheNeikos/rust,andars/rust,XMPPwocky/rust,gifnksm/rust,ruud-v-a/rust,cllns/rust,zachwick/rust,KokaKiwi/rust,reem/rust,philyoon/rust,robertg/rust,philyoon/rust,kwantam/rust,kwantam/rust,carols10cents/rust,miniupnp/rust,aidancully/rust,aidancully/rust,jashank/rust,ruud-v-a/rust,reem/rust,aidancully/rust,pelmers/rust,GBGamer/rust,andars/rust,mdinger/rust,KokaKiwi/rust,aidancully/rust,zubron/rust,nwin/rust