clutter: Use va_marshallers for actor signals
If possible, GLib will try to use the va_marshaller to pass the signal
arguments, rather than unboxing into and out of a GValue
. This is much
more performant and especially good for often-thrown signals.
The original bug that adds g_signal_set_va_marshaller()
even mentions Clutter performance issues as a drive to
implement the va_marshaller in GLib (see
https://bugzilla.gnome.org/show_bug.cgi?id=661140).