[InstCombine] Fold (sub (xor X, (sext C)), (sext C)) => (select C (neg X), X) (#79417)

This is useful when computing absdiff.

Correctness prove: https://alive2.llvm.org/ce/z/eMbxps,
https://alive2.llvm.org/ce/z/SNCWJe

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Co-authored-by: Yingwei Zheng <dtcxzyw@qq.com>