* Retry failed roots on refresh
* Don't prevent retry after error -> render(null) special case
The check wasn't very resilient because in Concurrent Mode it looks like we can get further follow-up commits even if we captured an error. So we can't reliably distinguish the case where after an error you _manually_ rendered null.
Retrying on an edit after a tree failed _and_ you rendered null in the same tree seems fine. It's also very unlikely a pattern like this actually exists in the wild.
* Track mounted roots via DevTools Hook
* Add helper utilities to the runtime
These utilities will likely be needed by all module systems, so let's just put them here.
* Wrap more things in __DEV__
* Fix tests to also be DEV-only
Dan Abramov