dillon1000/react

[Fiber] Gate Update flag on BeforeMutationMask on flags (#31921)

We're currently visiting the snapshot phase for every `Update` flag even
though we rarely have to do anything in the Snapshot phase.

The only flags that seem to use these wider visits is
`enableCreateEventHandleAPI` and `enableUseEffectEventHook` but really
neither of those should do that neither. They should schedule explicit
Snapshot phases if needed.