[llvm] [LLVM][C API] Support Value extraction from a MetadataAsValue. (PR #105501)

[Tim Besard via llvm-commits]

maleadt wrote:

@nikic This and https://github.com/llvm/llvm-project/pull/105521 should be good to go, could you review?

I have more bits of functionality to upstream from LLVM.jl, so let me know if there's a different workflow you prefer.

https://github.com/llvm/llvm-project/pull/105501