Add ability to make button labels match current keymap layout

[trigg]

requires #15
to be merged first

Huge overhaul.

Requires:

• xkbcommon
• xkbregistry
• input_method_v2 workaround (needs to be made optional)
• wayfire IPC to change between layouts (possibly make optional)

switches to other language/layout and switches to shift versions of buttons. Does not currently detect or respect hardware caps/shift/alt etc

includes two layouts currently:

• ANSI
• ISO

Problems:

• Hard requires input-method-v2. This is great for some places where clicking a text entry allows us to auto-show and navigate away hides. But a lot of things don't use it, so we probably need an option or an IPC method to show OSK.
• Hard requires IPC. We should probably soft require it and simply not update to other layers when in use on other wlroots envs
• Would like either a wl protocol or IPC to convey hardware modifiers being pressed/locked etc. Currently we track state ourselves and ignore hardware

TODO:

• Use Hint to show numpad when necessary, not generic input

• Use input_method_v2 to implement an autocorrect/suggest

• Find a cross-language autocorrect/suggest library. Make it optional

• Visual feedback for modifiers still broken

What is tested:

• GTK4+layer shell.
• shift modifier capitalises
• ctrl-c in terminal
• opening on GTK4 text entries automatically
• closing when clicking away