[llvm] [AArch64][GlobalISel] Add legalisation to G_EXRACT_SUBVECTOR (PR #207956)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Could you add some specific tests using llvm.extract.subvector? With strange types in them to make sure they do not crash.

https://github.com/llvm/llvm-project/pull/207956