[clang] [Clang] Add `__builtin_experimental_vectorcompress` (PR #102476)

[Lawrence Benson via cfe-commits]

lawben wrote:

Makes sense. I'll try to add the logic for the reamining SVE types in the next few days. I've been working on x86 instruction selection for this. I'll wait with this PR until both ARM and x86 are supported.

https://github.com/llvm/llvm-project/pull/102476