[clang] [CIR][AArch64] Implement vqshrun_n NEON builtin (PR #195080)

[Jiahao Guo via cfe-commits]

https://github.com/E00N777 commented:

Thank you very much for your contribution. I found a few nits – could you please fix them?

https://github.com/llvm/llvm-project/pull/195080