applets/swkbd: Implement the Qt Software Keyboard frontend

The Qt Software Keyboard frontend attempts to mimic the software keyboard rendered by the Nintendo Switch.
This frontend implements multiple keyboard types, such as the normal software keyboard, the numeric pad software keyboard and the inline software keyboard.
Keyboard and controller input is also supported in this frontend.
Keyboard input is handled as native keyboard input, and so the on-screen keyboard cannot be navigated with the keyboard arrow keys as the arrow keys are used to move the text cursor.
Controller input is translated into mouse hover movements on the onscreen keyboard or their respective button actions (B for backspace, A for entering the selected button, L/R for moving the text cursor, etc).
The text check dialogs can also be confirmed with controller input through the use of the OverlayDialog

Massive thanks to Rei for creating all the UI for the various keyboards and OverlayDialog. This would not have been possible without his excellent work.

Co-authored-by: Its-Rei <kupfel@gmail.com>