Add case to capture enum subtype reduction (addresses #35867)

[lawrencecraft]

Describe your changes

I've added a few tests to address the behavior described in #35867. The issue itself is fixed, but these tests will help catch regressions. Once this is merged the bug should be able to be closed.

Testing performed

I added cases for lots of permutations of this subtype reduction and checked the output to ensure the correct types were being returned. Everything looked good, including Typescript cleverly narrowing to unions of enums when values are falsy and the || operator would filter them out.

Thanks to @acutmore and @mkubilayk for the reviews and help on this!

Fixes #35867

[ghost]

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[RyanCavanaugh]

Oops, please sign the CLA so I don't have to revert that...

[mkubilayk]

@RyanCavanaugh CLA bot used to auto-accept PRs coming from the Bloomberg fork. Do you know if anything changed related to that? We have seen it not working on this PR and also in #49649, #49639, #49636.

[RyanCavanaugh]

That happens to be the thing I'm working on right now 😅