[SDAG] Add test for DAGCombiner multiple result commutative CSE

This commit adds a test for DAGCombiner commutative CSE on
nodes with multiple results (UMUL_LOHI). In this commit it
asserts the lack of CSE, a later commit will demonstrate
the CSE in the changed assertions.

Signed-off-by: Itay Bookstein <ibookstein@gmail.com>

Reviewed By: barannikov88

Differential Revision: https://reviews.llvm.org/D129905