Provide event hooks into the FBT API. about fbt

[jrwats]

Missing translations
@fruchtose, missing translations would be most appropriate at build-time when building translations (the work done in the translate script). For the runtime, we have added a few hooks as of 0.11.0, including the ability to override the result returned from the fbt._(...) runtime call 5ba6790

A note on implementation
We explicitly stayed away from an actual eventing mechanism and instead went with explicit callbacks due to the heavyweight nature of eventing machinery. Given that fbt is going to show up almost anywhere we have text, we want to try and ensure it stays performant and brings in as few modules as possible.

Real time data reporting / string lookup
I'd encourage checking out FbtHooks.logImpression, it's probably what you want to take advantage of.

Language lookup
I'd question whether this should be done in FBT. I'm not opposed to necessarily adding another hook for this, but it's expected that the application layer is going to be calling into FBT to switch languages/locales - not the other way around, so I'd question the value there. Let me know your thoughts.

If you have any other hooks you'd like to see, or internals into which you'd like more introspection, please let us know. I'm going to close this for now, but feel free to reopen.