[clang] [CIR] Upstream vec shuffle builtins in CIR codegen (PR #169178)

[Hendrik Hübner via cfe-commits]

HendrikHuebner wrote:

Nice work, could you break this up into smaller PRs?
For the builtins without test coverage in the incubator, please implement tests as well. Just take the other tests you upstreamed here as inspiration.

https://github.com/llvm/llvm-project/pull/169178