[clang] [llvm] [AArch64] Introduce new armv9.6 features (PR #111677)

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Lukacma wrote:

@jthackray @CarolineConcatto  Regarding using Armv9.6-A in feature descriptions, I am bit on the fence here. On the hand, I think it would make it clearer, in what architecture extension these features has been introduced, but on other hand these features can also be used with Armv9.5-A architecture and that might lead to user confusion as they might think these features are only available from Armv9.6-A  onwards. In the past, some feature used architecture extension names in their description and some didn't so not sure if there is any precedens here. In any case it might good to be consistent here.

https://github.com/llvm/llvm-project/pull/111677