refactor(android): Cleanup Keyman Engine for Android APIs

[darcywong00]

Holding issue for the thorough deep clean of Keyman Engine API's (implement in 19.0)

Among the growing list:

• cleanup setBannerOptions() - See discussions on fix(android): Cleanup setBannerOptions() API call #13567

Shared preferences should be managed through an API:

• Move language preference keys to apps to manage change(android/engine): Move language preference keys to apps to manage #4444
• Preference key names should not be resource strings chore(android): preference key names should not be resource strings #13633

[darcywong00]

Tentatively will schedule a week of face-to-face design meetings in PNH late 2025 to do some cleanup