[llvm] [AArch64] Add cost model for @experimental.vector.match (PR #118512)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm approved this pull request.

One point to consider but otherwise this looks good to me.

Perhaps it's worth adding a shortcut for `experimental_vector_match` to the common `getIntrinsicInstrCost()` implementation that simply calls onto `getTypeBasedIntrinsicInstrCost()` because otherwise the default case ends up calculating a redundant secularisation cost.

https://github.com/llvm/llvm-project/pull/118512