[DAGCombiner] Combine (fshl A, B, S) | (fshr C, D, BW-S) --> (fshl (A|C), (B|D), S) (#180889)
This is similar to the FSHL/FSHR handling in
hoistLogicOpWithSameOpcodeHands.
Here the opcodes aren't exactly the same, but the operations are
equivalent.
Fixes regressions from #180888