support for auto-hidden windows to resize

Summary:
auto hidden windows were shown again when their geometry
changed, this was done for being as easy as possible as
the unhide zone changed, but the behavior looked very
annoying as autohide panels with an self resize taskbar
would unhide themselves every time any window gets open
or closed.
This makes the edge keep track of
windows that can resize/move themselves while auto hidden

Test Plan:
a self-resizing autohidden panel with a taskbar in it doesn't auto unhide
anymore when a window is opened or closed.
the unhide area gets properly updated

Reviewers: graesslin, #plasma

Reviewed By: graesslin, #plasma

Subscribers: luebking, plasma-devel, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D4718