auto merge of #20185 : csouth3/rust/dlist-deprecate, r=alexcrichton
auto merge of #20185 : csouth3/rust/dlist-deprecate, r=alexcrichton

This PR deprecates the `DList::ListInsertion` trait, in accordance with rust-lang/rfcs#509.  The functions which were previously part of the ListInsertion impl for `DList::IterMut` have been moved to be inherent methods on the iterator itself, and appropriate doctests have been added.

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