QPlatformInputContextPlugin
Gtk.IMContext
zwp_input_method_context_v1
zwp_input_method_v2
xim

zwp_text_input_v3?
send backend: zwp_virtual_keyboard_v1?

## Scheme

Note: I'm not a Scheme professional, this is an experiment, feel free to
suggest improvements.

Concepts:

- Layout - a procedure that returns a UI layout


API:

popup.setLayout(layout: Layout | null)

keyboard.setLayout(layout: Layout | null)