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

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space commented:

Please find fresh comments inline.

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