Add the layout `destroy` and `change` events.
When a layout is destroyed, detach is from the wlr_cursor.
When a layout is changed, warp the cursor to the closest layout boundary.
An output layout consists of a mapping of outputs to their position in a global
coordinate system that usually cooresponds to the output position in physical
space in front of the user.
Add an example that allows configuration of an output layout and demonstrates
its boundaries with a bouncing image.