Also added trait bounds to Widget since its trait object has been replaced by
BaseWidget.

Swapped us over to a `KayakContextRef` which better handles some things.

Border

[RFC 1] Widget Restructuring

Draggable Windows

Added the CursorEvent struct to the cursor-related enum variants on
EventType

Also changed how PartialEq and Hash work for EventType. They no longer
consider the inner variant data

Added UI Detection

Improve Focus Management

Also added to KayakContext (as interface for Bevy) and to
EventDispatcher (where it's managed)

Font measure