inputmethod: replace enablement with visibility modes for the virtual keyboard
The modes are
- never show the virtual keyboard
- only show it with non-mouse inputs
- show it with all input devices
The input method stays enabled in all cases, since we don't know if it's actually (only) a virtual keyboard or if it handles events from physical keyboards as well.
Co-authored-by: Xaver Hugl xaver.hugl@kde.org CCBUG: 466948
Supersedes !8509 (closed). The changes are mostly minor, with the exception that the input method never gets disabled by the mode, so that keyboard-based input methods continue to work independently of the virtual keyboard. If a user wants to disable it entirely, they can just set the input method to "none" in system settings.