This will help make the init procedure safer, by limiting the number of Rust objects that need to be carried to the C side and may be mangled on the way there.
The second benefit is that it allows outputs to become part of new state management.
Control and Alt are special in that they aren't expected to switch levels, and so don't need to change what characters are output.
Use in layouts by adding `modifier: Control` or `modifier: Alt` in place of `text: "foo"`.
The latching of the modifier will force the keyboard to emit raw key presses and prevent it from outputting text.
