[macOS] QMacToolBar doesn't support new styles in macOS Big Sur

QMacToolBar buttons are misplaced and look broken in a Qt app

Strangely enough: when using XCode 11.3, it's fine. See screenshots

Update: the reason is new NSWindowToolbarStyle
By default it uses NSWindowToolbarStyleAutomatic whilst most users expect traditional approach.
Just wrote a quick workaround class for it to avoid modifying Qt. Do recommend though adding this enum/get/set to the QMacToolbar class.