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