D9967: Acknowledge the server side deco mode in WaylandServer not ShellClient

[Nathaniel Graham]

Restricted Application edited projects, added Plasma; removed KWin.

REPOSITORY
  R108 KWin

BRANCH
  deco-acknowledge-server-5.12

REVISION DETAIL
  https://phabricator.kde.org/D9967

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