Don't snap to auto-hidden panels
Summary:
When moving windows we don't want to snap against not visible windows
like auto-hidden panels.
BUG: 365892
FIXED-IN: 5.8.4
Test Plan: So far only auto-test, manual test will follow.
Subscribers: plasma-devel, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D3225