[clang] [ARM][AArch64] Add missing Neon Types (PR #126945)

[David Green via cfe-commits]

davemgreen wrote:

I was discussing with @tmatheson-arm and he said I could take this over. I've updated this branch (apparently that does work), trying to address the issues and clean things up a bit. The new types are not longer a keyword, but that seems to be OK providing we mark them as implicit typedefs.

https://github.com/llvm/llvm-project/pull/126945