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

[Andrzej Warzyński via cfe-commits]

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

LG % nits

How about the other intrinsics from https://arm-software.github.io/acle/neon_intrinsics/advsimd.html#split-vectors-1?

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