Auto merge of #97863 - JakobDegen:bitset-choice, r=nnethercote

`BitSet` related perf improvements

This commit makes two changes:
 1. Changes `MaybeLiveLocals` to use `ChunkedBitSet`
 2. Overrides the `fold` method for the iterator for `ChunkedBitSet`

I have local benchmarks verifying that each of these changes individually yield significant perf improvements to #96451 . I'm hoping this will be true outside of that context too. If that is not the case, I'll try to gate things on where they help as needed

r? `@nnethercote` who I believe was working on closely related things, cc `@tmiasko` because of the destprop pr

Author: bors