screenedge: Don't unhide panel from old edges
The panel is unhided when the screen is rotated, which is not convenient for 2-in-1 laptop users.
x11client: Use QTimer::singleShot in m_edgeGeometryTrackingConnection
frameGeometryChanged will be emitted before and after the panel is
moved to the edge, but we don't want to call reserve(...) before the
panel is moved.
xdgshellclient: Add a small delay before calling
frameGeometryChanged is emitted only once after a screen
is rotated and before the panel is moved to any edge, so set a small
delay to get the correct geometry of a screen.
This is hacky because the required delay could vary on different devices. I don't know if it's intended not to emit
frameGeometryChanged again after the panel is moved (which changes the geometry of a screen).