dillon1000/react

Re-arrange main ReactFeatureFlags module (#23350)

@sebmarkbage and I audited the feature flags file to review the status
of each feature or experiment. Based on that, I've added some more
comments to the main ReactFeatureFlags module and rearranged them
into groups.

I haven't changed the value of any flags, yet. There are a few we're
going to land but I'll do them as separate PRs.