QWindow: setting flags on maximized window exits maximized state and causes inconsistencies

Removing the Qt::WindowCloseButtonHint from the window flags of a maximized window triggers some unexpected behaviour:

• Platform window leaves the maximized state (indicated by the changing window decorations) but is resized to fill the entire screen (this also means the original geometry pre-maximize is lost).
• QWindow::windowState(s) still reports Qt::WindowMaximized.