[llvm] [GlobalISel] Fold G_SHUFFLE_VECTOR with a single element mask to G_EXTRACT_VECTOR_ELT (PR #65342)

[Jay Foad via llvm-commits]

https://github.com/jayfoad approved this pull request.

LGTM if the AArch64 maintainers are OK with the slight regression.

https://github.com/llvm/llvm-project/pull/65342