[clang] [CIR][AArch64] Implement vget_lane_bf16 and vgetq_lane_bf16 builtins (PR #186866)

[Jiří Filek via cfe-commits]

================

----------------
fileho wrote:

@banach-space I have resolved the conflict. Since all six related builtins are now implemented, I have merged them into a single block to be consistent with my previous version and ARM.cpp. Let me know if I should change it

https://github.com/llvm/llvm-project/pull/186866