Summary:
This change implements support for the wl_surface events enter and
leave. Those events are emitted whenever a surface becomes visible on
an output by e.g. mapping the surface, moving or resizing it. Similar
the leave is sent whenever the surface is no longer on an output.

The server side is not yet fully complete yet. It also needs to emit
when the client binds the output another time and needs to send a
leave before destroying the output.

Reviewers: #plasma_on_wayland

Subscribers: plasma-devel

Tags: #plasma_on_wayland

Differential Revision: https://phabricator.kde.org/D2528