D15421: [server] Add surface data proxy mechanism

[Roman Gilg]

romangg added a dependent revision: D15627: [xwl] Drag and drop between 
Xwayland and Wayland native clients.

REVISION DETAIL
  https://phabricator.kde.org/D15421

To: romangg, #kwin
Cc: kde-frameworks-devel, michaelh, ngraham, bruns