[clang] [llvm] Move several vector intrinsics out of experimental namespace (PR #88748)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> I don't know what the policy is for promoting intrinsics from experimental to first-class or if it's documented anywhere (?), but I would expect this to be accompanied with an RFC / announcement on Discourse.

I don't remember any intrinsic ever making the move out of experimental. It seems to be a permanent prefix 

https://github.com/llvm/llvm-project/pull/88748