Register the bundle regardless of whether Fast Refresh is on

Summary:
We want to move to a world where Fast Refresh is on by default. As a first step, we can register the bundle early. This means we'll start receiving hot updates via the socket even if Fast Refresh is off. We'll just be ignoring those.

Anecdotally people with Fast Refresh on have had good experience even with invasive changes like branch switches. So this seems like a good way to test the waters further. It's also a prerequisite to unlocking a nicer experience where you can turn it on anytime and "catch up" on the changes you've missed. (That's out of scope of this diff.)

Reviewed By: cpojer

Differential Revision: D16344019

fbshipit-source-id: 6e5f8278909810b32c80e0af010251c876e4313b