D7955: Move X11-only specific part of EffectsHandlerImpl to x11 platform plugin

[Martin Flöser]

graesslin added a dependency: D7846: [tabbox] Drop the passing to Effects in 
X11 Filter.

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D7955

To: graesslin, #kwin, #plasma
Cc: plasma-devel, kwin, bwowk, ZrenBot, progwolff, lesliezhai, ali-mohamed, 
hardening, jensreuterberg, abetts, sebas, apol, mart