Summary:
This protocol allows to indicate that a wl_surface should inhibit idle
actions such as DPMS, screen locking if the surface is visible.

The protocol is quite simple: it just creates an IdleInhibitor for a
Surface. If such an IdleInhibitor exists the Surface is considered to
inhibit idle.

On the server side it is also exposed like that through the API. The
IdleInhibitorInterface is private to the library and only
SurfaceInterface is extended to expose whether it currently inhibits
idle.

CCBUG: 385956

Test Plan: New test case added

Reviewers: #frameworks, #kwin, #plasma_on_wayland

Subscribers: plasma-devel

Tags: #plasma_on_wayland, #frameworks

Differential Revision: https://phabricator.kde.org/D8396