Remove window decorations when fullscreen

Fix a compatibility issue with metacity 3.36, where SDL and the WM
might keep fighting for the window flags in an endless loop and/or in
an inconsistent window mode.

Upstream reference: https://gitlab.gnome.org/GNOME/metacity/-/issues/11

src/player/SDLWindow.cpp

@@ -62,7 +62,7 @@ SDLWindow::SDLWindow(const DisplayParams& dp, const WindowParams& wp, GLConfig g
     }
     unsigned int flags = SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL;
     if (dp.isFullscreen()) {
-        flags |= SDL_WINDOW_FULLSCREEN;
+        flags |= SDL_WINDOW_FULLSCREEN | SDL_WINDOW_BORDERLESS;
     }
     if (!wp.m_bHasWindowFrame) {
         flags |= SDL_WINDOW_BORDERLESS;