[clang] [Clang][AArch64] Allow FP8 Neon vector types to be used by __builtin_shufflevector (PR #119031)

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CarolineConcatto wrote:

Hi @efriedma-quic,
the reason I implement as BuiltinType is because the MFloat8x8 and MFloat8x16 are a target specific types.  So I only changes target specific files to add the new types. Like we did for the sve types, they are also builtin types.

https://github.com/llvm/llvm-project/pull/119031