Fix the seek bar dragging issue

[rdbende]

Using a GtkGestureClick here is not possible, as GtkRange's internal gesture controller claims the button press event, and thus the released signal doesn't get emitted. Therefore I added this hacky solution that gets its internal GtkGestureClick, and appends the seek bar's handlers to that.

Ideally this would be fixed in GTK, and GtkRange would forward these signals, so we wouldn't need this hack. Here's the issue about it on the GTK GitLab repo: https://gitlab.gnome.org/GNOME/gtk/-/issues/4939