Rollup merge of #69814 - jonas-schievink:gen-ret-unw, r=Zoxc

Rollup merge of #69814 - jonas-schievink:gen-ret-unw, r=Zoxc

Smaller and more correct generator codegen

This removes unnecessary panicking branches in the resume function when the generator can not return or unwind, respectively.

Closes https://github.com/rust-lang/rust/issues/66100

It also addresses the correctness concerns wrt poisoning on unwind. These are not currently a soundness issue because any operation *inside* a generator that could possibly unwind will result in a cleanup path for dropping it, ultimately reaching a `Resume` terminator, which we already handled correctly. Future MIR optimizations might optimize that out, though.

r? @Zoxc