[clang] [Clang] [NFC] Introduce `DynamicRecursiveASTVisitor` (PR #105195)

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cor3ntin wrote:

This is a very impressive piece of work!
I think we are looking at a non-trivial choice: 

- Do we make clang faster to compile for ourselves, or slightly faster for everyone? My initial thinking is that clang is run orders of magnitude more often than it is compile, and so improving compile times might not be the best tradeoff? 
It would certainly be nice _for ourselves_.

We should also look at how PGO/BOLT affect both of these options. (Note sure how one does that though
https://github.com/llvm/llvm-project/issues/65010).


https://github.com/llvm/llvm-project/pull/105195