This adds a simple VoidCallbackAction and VoidCallbackIntent that allows configuring an intent that will invoke a void callback when the intent is sent to the action subsystem. This allows binding a shortcut directly to a void callback in a Shortcuts widget.

I also added an instance of VoidCallbackAction to the default actions so that simply binding a shortcut to a VoidCallbackIntent works anywhere in the app, and you don't need to add a VoidCallbackAction at the top of your app to make it work.