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

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

Since other PRs would benefit from these changes, and since I’ll be away next week, I took the liberty of landing this.

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