This commit was started by copying `addons/escoria-ui-9verbs` as the
basis for `addons/escoria-ui-keyboard-9verbs`. It was then amended to
wire up keyboard shortcuts for each verb using the new
`register_custom_input_handler()` API.
Note that `addons/escoria-ui-keyboard-9verbs/input_map.gd` introduces
one action per verb and provides a `add_actions_to_input_map()`
function to add the actions to the `InputMap`. The `_process_input()`
function in `game.gd` is responsible for mapping each action to the
appropriate call to `verbs_menu.on_action_selected()`.
This introduces a new API on `ESCInputsManager` that makes it
possible to inject custom logic for processing input events.
An example of how to use this API will be introduced in a
separate commit as part of
https://github.com/godot-escoria/escoria-demo-game/pull/503
via a new plugin, `addons/escoria-ui-keyboard-9verbs/`,
which shows how this can be used to add support for keyboard shortcuts
to select a specific verb.
Michael Bolin