[Refactor] clean up union explosion case
[Refactor] clean up union explosion case

Summary: We blow up unions in all kinds of places; this moves all of them into one function call.

Reviewed By: gabelevi

Differential Revision: D18023891

fbshipit-source-id: ca5174344064c4a75f457062a1f2068694099128

mroch/flow,facebook/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,mroch/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,samwgoldman/flow