[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 , any luck applying my diff? If you are still struggling, I can complete this PR for you.
> > Thank you, -Andrzej
> 
> Hi, yes please! I'd really appreciate that.

No problem. The only available approach for me to take here is to close this PR and open a new one. I will add you as a co-author.

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