Slim down QPlatformHeaders

QWaylandWindowFunctions

• Has setDeSync/setSync/isSync, but the backend implementation in WaylandSurfacePrivate::Subsurface is just "// TODO: sync/desync implementation".
  Is this dead code? Should we remove it? If we keep it, why is it setSync and setDeSync? From reading https://wayland.freedesktop.org/docs/html/apa.html this looks like a mode, shouldn't it be a setSync(bool), or a setSync(enum SyncMode)? tvete paeglis 

QEglFSFunctions

• vsp2 support. Is this eglfs device integration alive? Was added as tech preview in 2017. lagocs

QWindowsWindowFunctions

• setTouchWindowTouchType -> QWindowsWindow
• setHasBorderInFullScreen/Default -> QWindowsWindow
• setWindowActivationBehavior -> Needed? If so QWindowsApplication
• isTabletMode: Per app (or system) setting (https://docs.microsoft.com/en-us/uwp/api/windows.ui.viewmanagement.uiviewsettings?view=winrt-19041) -> QWindowsApplication
• setWinTabEnabled -> QWindowsApplication

Are any of the windows functions no longer relevant?