_NET_WM_SYNC_REQUEST resizing support

[Antoine Martin]

Long overdue.
Not going to help with applications that do not support it (I'm looking at you Java: #705), but will probably help with many other well behaved applications:
​Window Manager Protocols: _NET_WM_SYNC_REQUEST

[Antoine Martin]

Problem is that ​gdk.Window enable-synchronized-configure is that Toplevel GTK+ windows automatically use this protocol.

And there is no easy way to disable this, here's the check we could hijack:

  impl = GDK_WINDOW_IMPL_X11 (((GdkWindowObject *)window)->impl);
  if (!impl->use_synchronized_configure)
    return;

By accessing the underlying X11 window object.
Problem is that the call to gdk_window_configure_finished is embedded deep in the gtk_window_move_resize and gtk_window_configure_event handlers.

And so it might just be easier to not use GTK at all...

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/723