Add test case for Split2QUnitaries with swap equiv combined with ElidePermutations

[mtreinish]

What should we add?

As was discussed in: #13531 there was a small direct test coverage gap identified to validate in isolation that when we have another pass that introduces routing permutations running in addition to Split2QUnitaries. We have indirect coverage of this case via the full transpiler pipeline, but having a more direct test in isolation will help debug issues if we encounter them in the future. #13531 didn't wait for this test as to not block it, especially because it had a bug fix embedded in it. This issue is to track adding that test case so we don't forget to add it.