[clang] [CIR][AArch64] Support BF16/FP16 NEON types and lower vdup lane builtins (PR #187460)

[Andrzej Warzyński via cfe-commits]

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

Thank you for sending this and for your comprehensive summary!

The approach taken makes sense. I will take one more look later to see whether we can layer things better. In the meantime, I am posting a few requests regarding tests.

https://github.com/llvm/llvm-project/pull/187460