[clang] [CIR][AArch64] Upstream vrshrd_n_s64/u64 and vrshr_n_v vector rounding shift right (PR #185992)

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

@ArfiH , are you able to resolve the merge conflicts? I have merged a few PRs recently, so that is likely my fault. Hopefully it won't be too hard to resolve and we will be able to merge this shortly. Thanks for pushing on this!

https://github.com/llvm/llvm-project/pull/185992