[InstCombine] Fold (sext bool X) * (sext bool X) to zext (and X, X)

InstCombine didn't perform (sext bool X) * (sext bool X) --> zext (and X, X) which can result in just (zext X). The patch adds regression tests to check this transformation and adds a check for equality of mul's operands for that case.

Differential Revision: https://reviews.llvm.org/D104193