[llvm] [IR] Allow type change in ValueAsMetadata::handleRAUW (PR #76969)

[Jeremy Morse via llvm-commits]

jmorse wrote:

I feel like this is well motivated, and as you say there aren't actually any parts of LLVM that rely on ValueAsMetadata types for correctness (AFAIUI). Would I be right in thinking that this only enables use-cases that are directly calling ValueAsMetadata::handleRAUW, because performing a normal RAUW will do the usual type checks?

CC @OCHyams and @SLTozer as they've touched this area more recently than me.

https://github.com/llvm/llvm-project/pull/76969