[SDAG] Handle A and B&~A in haveNoCommonBitsSet()

This is the DAG variant of D124763. The code already handles the
general pattern, but not this degenerate case.

This allows folding A + (B&~A) to A | (B&~A) which further holds
to A | B.

Handling on the SDAG level is needed because in the motivating
case the add is actually a getelementptr, which only gets converted
into an add on the SDAG level. However, this patch is not quite
sufficient to handle the getelementptr case yet, because of an
interfering demanded bits simplification.

Differential Revision: https://reviews.llvm.org/D124772

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