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

[David Sherwood via llvm-commits]

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

LGTM! Thanks for this @rj-jesus. The generic costs in BasicTTIImpl seem sensible, and if the costs in AArch64TargetTransformInfo turn out to be too conservative we can always change them later.

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