Summary:
From feedback we got it seems that not all users agree to games and
other applications blocking compositing. Some users prefer to have
compositing always on even if this gives a small performance penelity.

This change introduces a dedicated config option to specify whether games
are allowed to block compositing. By default this option is enabled.

The setting can be overwritten with a window specific rule. So usecases
like all windows except this very specific one are supported.

In the user interface the config option is shown where previously the
unredirect fullscreen option was shown.

Test Plan:
Run a game which should block compositing, verified it blocks.
Changed the setting, run the game again, verified it doesn't block. And
once more for with allowing to block.

Reviewers: #kwin, #plasma_on_wayland, #vdg

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D2584