Add a valgrind suppression file
Like the GLib suppression file, it would be useful if Pango shipped with a suppression file which users could use to suppress valgrind reports about deliberate leaks. After testing with Pango master, there are some actual leaks or deliberate leaks remaining here: glib#1879 (comment 587579)
Log here: https://gitlab.gnome.org/GNOME/glib/uploads/e0cc80c89b1f3195f0b234ab746f056b/out, although this might include some reports which aren’t relevant to Pango