keybind widget

[hecrj]

This PR introduces a brand new widget: keybind.

A keybind widget can be used to trigger a click interaction on its contents when a certain Hotkey is pressed.

A Hotkey is a keyboard combination: a key, some modifiers, and an optional location. By default, hotkeys use keyboard::Modifiers::COMMAND as the trigger modifiers.

For instance:

keybind('s', button("Save").on_press(Message::Save))

This will display a save button that can be clicked with the mouse and also by pressing Ctrl+S (or ⌘+S on macOS). In both instances, a Save message will be produced.

[hecrj]

I am scratching this idea.

Since keybind listens to key presses unconditionally, it is possible to write UIs with conflicting keybinds very easily.

The current Subscription approach is superior because the most natural design encourages a single source of truth for key presses.