Auto merge of #26659 - nagisa:cas-docs, r=alexcrichton
Auto merge of #26659 - nagisa:cas-docs, r=alexcrichton

Namely:

* Change parameter `old` to read `current` so it is clearer what the argument refers to (originally
   suggested `expected`, but shot down by Steve);
* Add some formatting and fix some mistakes like referring to the method as `swap` rather than
  `compare_and_swap`.

zubron/rust,nwin/rust,graydon/rust,GBGamer/rust,jashank/rust,jashank/rust,nwin/rust,vhbit/rust,dwillmer/rust,dwillmer/rust,jroesch/rust,l0kod/rust,jashank/rust,jashank/rust,graydon/rust,aidancully/rust,reem/rust,zubron/rust,aidancully/rust,mvdnes/rust,aidancully/rust,l0kod/rust,KokaKiwi/rust,jashank/rust,GBGamer/rust,KokaKiwi/rust,zubron/rust,pshc/rust,jroesch/rust,nwin/rust,l0kod/rust,zubron/rust,nwin/rust,GBGamer/rust,dwillmer/rust,graydon/rust,graydon/rust,l0kod/rust,vhbit/rust,graydon/rust,mvdnes/rust,pshc/rust,mvdnes/rust,jroesch/rust,dwillmer/rust,reem/rust,reem/rust,GBGamer/rust,pshc/rust,jroesch/rust,zubron/rust,vhbit/rust,KokaKiwi/rust,aidancully/rust,GBGamer/rust,pshc/rust,l0kod/rust,l0kod/rust,pshc/rust,zubron/rust,mvdnes/rust,nwin/rust,l0kod/rust,jroesch/rust,pshc/rust,zubron/rust,pshc/rust,dwillmer/rust,nwin/rust,vhbit/rust,vhbit/rust,vhbit/rust,jashank/rust,reem/rust,KokaKiwi/rust,graydon/rust,GBGamer/rust,vhbit/rust,reem/rust,jashank/rust,reem/rust,GBGamer/rust,pshc/rust,GBGamer/rust,jroesch/rust,KokaKiwi/rust,dwillmer/rust,jroesch/rust,dwillmer/rust,vhbit/rust,nwin/rust,mvdnes/rust,mvdnes/rust,l0kod/rust,dwillmer/rust,aidancully/rust,KokaKiwi/rust,jroesch/rust,zubron/rust,nwin/rust,aidancully/rust,jashank/rust