[llvm] [VectorCombine] Allow shuffling between vectors the same type but different element sizes (PR #121216)

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ParkHanbum wrote:

@RKSimon Thank you for your review. Thanks to you, the patch seems to be almost complete. Could you please review this PR as well? https://github.com/llvm/llvm-project/pull/119139

https://github.com/llvm/llvm-project/pull/121216