Add support for text-input

[emersion]

This will allow IMEs/virtual keyboards to work properly with swaylock.

[stacyharper]

I discovered I was able to show wvkbd, our virtual keyboard, above swaylock if we use the overlay layer. Then we have to start wvkbd before swaylock. But then, we still ~~can~~ cant click on the virtual keyboard.

Is it something we expect to be able to ?

edit: maybe that swaylock is seting exclusive zone everywhere ? so that virtual keyboard are impossible by design ?