[OSK] Implement standard/enhanced keyboard handler (#1338)

[OSK] Implement standard/enhanced keyboard handler (#1338)

- Add the respective standard keyboard resource.
- Implement the standard/enhanced keyboard dialog switcher.
- Implement save/load handler.
- Move the warning box conditinal check (bShowWarning) to wWinMain application entry point (this will prevent the modal welcome box from displaying each time the user switches into another dialog).

CORE-14428