[InstSimplify] Fold and/or using implied conditions

This adds two conjugated folds:

 * A | B -> B if A implies B (https://alive2.llvm.org/ce/z/R6GU4j)
 * A & B -> A if A implies B (https://alive2.llvm.org/ce/z/EGMqyy)

If A and B are icmps themselves, we will usually fold this through
other logic already (though the tests show a couple additional cases
we previously missed). However, isImpliedCond() also supports A
being of the form X & Y, which allows us to handle cases like
(X & Y) | B where X implies B. This addresses the regression from
D125398.

Something that notably doesn't work yet is the (X | Y) & B case.
This is due to an asymmetry in the isImpliedCondition()
implementation that will have to be addressed separately.

Differential Revision: https://reviews.llvm.org/D125530