Notify of screen geometry changes only after DesktopView has updated

Currently updating the DesktopView geometry and emitting signals notifying of changes to screen geometry are connected independently to QScreen::geometryChanged(), while screenGeometry() as well as availableScreenRect() and availableScreenRegion() depend on the DesktopView geometry. The incorrect order of slots being called causes the task manager to behave incorrectly on screen configuration changes, displaying either no windows or windows from a wrong screen. This also affects the desktop pager widget when configured to show the current desktop only.

BUG: 373075