Auto merge of #100089 - JakobDegen:no-invalidate-visitor, r=tmiasko

Add option to `mir::MutVisitor` to not invalidate CFG.

This also applies that option to some uses of the visitor. I had considered a design more similar to #100087 in which we detect if the CFG needs to be invalidated, but that is more difficult with the visitor API and so I decided against it. Another alternative to this design is to offer an API for "saving" and "restoring" CFG caches across arbitrary code. Such an API is more general, and so we may eventually want it anyway, but it seems overkill for this use case.

r? `@tmiasko`

Author: bors