Use the size hint provided by the compositor to resize the window
associated with a Wayland toplevel surface.

A surface config moves through the following stages (each stage may hold
a different event):

1. Pending: In the process of being populated from separate Wayland
   events.

2. Requested: A fully formed config which hasn't been handled yet. A new
   finalized Pending event will always be promoted to a Requested event
   (so we will skip previous events if new ones arrive quickly enough).

3. Processing: A config that is being processed. When processing is
   done, we mark it with `wayland_surface_config.processed = TRUE`.

4. Current: The config has been acknowledged, i.e., we are promising to
   respect any implied content constraints.