[clang] Enable AST mutation in the constant evaluator (PR #115168)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

I added Sema callback into the new interpreter in 0b2d92e0fed41ee2428c3ef8b8369790a1279a21. I think it went smoothly, save for the fact that source locations are not always readily available there, but they are need to correctly emit diagnostics from Sema.

I invite @tbaederr to provide early feedback on my changes to the new constant interpreter.

https://github.com/llvm/llvm-project/pull/115168