fix(developer): require language tag when compiling keyboard package

Fixes #2998.

Three parts to this:

* The package compiler will now give a warning if a keyboard in a
  package does not contain any language metadata.

* Removed old canonicalization check during compile which is now handled
  better in `TPackageInfoRefreshKeyboards`.

* Reduced non-canonical BCP 47 tag warnings in
  `TPackageInfoRefreshKeyboards` to "info" so they do not block the
  build.

Point 3 above is one part of the outcome of our BCP 47 discussion at:
https://docs.google.com/document/d/1N5CkTX7tlLlmUB9Mbd-LblY1ch1e642XxlTasC_WE_Q/edit#heading=h.fiy983iliay5