[clang] [CLANG][AArch64]Add Neon vectors for mfloat8_t (PR #99865)

[Paul Walker via cfe-commits]

https://github.com/paulwalker-arm commented:

I can be persuaded if there are good reasons for the `TypeSpec` side to wait, but the the current placement of the typedefs looks wrong. 

https://github.com/llvm/llvm-project/pull/99865