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

[Maciej Gabka via cfe-commits]

mgabka wrote:

I was actually following this patch https://reviews.llvm.org/D127976 which promoted vector.insert/extract and there was no RFC for it.
My understanding is that these intrinsics are so heavily used in LLVM now so there is no need to call them experimental, moreover the auto upgrade ensures that the "experimental" name is still honoured.

My plan was to promote stepvector as well in separate PR.

I am happy to raise an RFC if you feel that it is worth it.

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