Fix the playback bar is not aligned to the bottom in the FSM on Linux

The reason why the playback panel is not aligned to the bottom in fullscreen mode on Linux is because the desktop environment panels (like taskbar, topbar, etc.) set struts that limit the area over which the top-level window can be moved programmatically. To get around this, we need to tell the window to ignore window manager hints (by setting the Qt::X11BypassWindowManagerHint flag) and manually limit its movement.

BUG: #22563 (closed)