Reapply [InstSimplify] Make simplifyWithOpReplaced() recursive (PR63104)

A similar assumption as for the x^x case also existed for the absorber
case, which lead to a stage2 miscompile. That assumption is not fixed.

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Support replacement of operands not only in the immediate
instruction, but also instructions it uses.

To the most part, this extension is straightforward, but there are
two bits worth highlighting:

First, we can now no longer assume that if the Op is a vector, the
instruction also returns a vector. If Op is a vector and the
instruction returns a scalar, we should consider it as a cross-lane
operation.

Second, for the x ^ x special case and the absorber special case, we
can no longer assume that one of the operands is RepOp, as we might
have a replacement higher up the instruction chain.

There is one optimization regression, but it is in a fuzzer-generated
test case.

Fixes https://github.com/llvm/llvm-project/issues/63104.