[http-client-csharp] rename UnionTypes in TypeFactory to UnionVariantTypes?

[ArcturusZhang]

We have a HashSet<string> UnionTypes in TypeFactory tracking the names of all existing union variant types.

Shall we rename it to UnionVariantTypes to avoid confusion?

[JoshLove-msft]

@ArcturusZhang can you clarify what the confusion would be? The naming matches the public InputUnionType.

[ArcturusZhang]

@ArcturusZhang can you clarify what the confusion would be? The naming matches the public InputUnionType.

First I thought this set is tracking the union types themselves. But actually this is tracking those variants.
For instance, we have a union A | B, the set should contain type A and type B, but not the union itself A | B.

I think this is here to make sure we would keep these variants in post processor - otherwise they would be trimmed off.
But I think these variants should have usages in the xml doc, would roslyn ignore these usages and we have to track them by ourselves?
Also this might be problematic because we did not ensure the model that encloses the union type has not been removed.