Slightly generalize simplifyAndOrWithOpReplaced() by allowing it to
perform simplifications (without creating new instructions) in multi-use
cases. This way we can remove existing patterns without worrying about
multi-use edge cases.
I've opted to change the general way the implementation works to be more
similar to the standard simplifyWithOpReplaced(). We perform the operand
replacement generically, and then try to simplify the result or create a
new instruction if we're allowed to do so.
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