Fixes and changes:
● When calculating the tab size, consider the actual tab icon size (which may rarely be different from PM_TabBarIconSize).
● Ensure correct menu blurring if the compositor kicks in with a short delay.
● Allow elided texts in task buttons of LXQt Panel.
● Prevent menus from switching screen with multi-screen setups.
● Don't add an arrow to a tool button with instant popup.
● Fixed an old problem in toolbars of dark-and-light themes.
● A key is added for the thickness of toolbar separators.
● A workaround for a bug in Qt5ct.