[llvm] [UniformityAnalysis] Add CallbackVH to keep UniformValues consistent on value deletion (PR #187658)

[Pankaj Dwivedi via llvm-commits]

PankajDwivedi-25 wrote:

I prototyped using AssertingVH as the set key to enforce this contract in debug builds, but it triggers ~168 test failures because existing passes (StructurizeCFG, SIAnnotateControlFlow, etc.) delete values after uniformity analysis without calling eraseValue().

My plan is to call eraseValue in those places in this patch itself.

https://github.com/llvm/llvm-project/pull/187658