feat(android): Spacebar text controls 🍒

Cherry-pick of a3ec34a3.

Relates to #949.

* Adds setSpacebarText() API to Keyman Engine for Android
* Adds displayName API to Keyman Engine for Android
* Sets default spacebar text to keyboard name for FirstVoices Keyboards
* Does not include the preference changes to Keyman for Android -- these
  will be surfaced as a feature in 15.0.