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

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space approved this pull request.

LGTM % final comments

Thank you for working on this! Do you have commit access? I can merge this once my final comment is addressed.

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