Auto merge of #71312 - wesleywiser:const_prop_bitset, r=Mark-Simulacrum
Auto merge of #71312 - wesleywiser:const_prop_bitset, r=Mark-Simulacrum

[ConstProp] Use a `BitSet<Local>` instead of `IndexVec<Local, bool>`

aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust