Auto merge of #65672 - ecstatic-morse:unified-dataflow-proto, r=pnkfelix
A single framework for gen-kill and generic dataflow problems
This is the prototype implementation discussed in rust-lang/compiler-team#202. You can read a high-level description of it in [the proposal](https://hackmd.io/@39Qr_z9cQhasi25sGjmFnA/Skvd9rztS) for that design meeting. This would eventually supersede the existing `BitDenotation` interface.
r? @ghost
cc @rust-lang/compiler (esp. @eddyb and @pnkfelix)