Panel auto hide support for Wayland panels

Summary:
This change implements auto-hide support for Wayland panels. To properly
test the screenedgeshowtest is reworked to support both X11 and Wayland
windows.

Reviewers: #kwin, #plasma_on_wayland, bshah

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D3080