[VectorUtils] Add helper to get list of metadata to propagate (NFC). (#135003)
Split off the logic to filter out metadata that should not be propagated
to a helper that populates a list with metadata kinds that should be
preserved.
The current version just uses is_contained on an array to check if a
metadata kind is supported. Given that most instructions will only have
a small number of metadata kinds to start with, this shouldn't be worse
than iterating over all kinds once and querying the instruction for
individual metadata kinds, which involves quite a bit of indirection.
I plan ot use this utility in a follow-up patch in other places as well.
PR: https://github.com/llvm/llvm-project/pull/135003