Summary:
Adds XDGV6 support for the kwin side.
Popup placement support is limited to the stuff v5 had,
a simple offset, rather than the awesome new positioner.
But Qt doesn't make use of it yet either.
Also ideally we should do all the positioning before sending the first
configure, but again Qt doesn't actually do anything with that anyway.
Also integrate pinging clients
Test Plan: gtk3-demo works nicely.
Reviewers: #plasma, graesslin, mart
Reviewed By: #plasma, graesslin
Subscribers: mart, graesslin, kwin, plasma-devel, #kwin
Tags: #plasma
Differential Revision: https://phabricator.kde.org/D6591
e492f9e298