This adds specific marshallers for all of the locations where a generic
marshaller is being used. It also provides va_marshallers to reduce the
chances that we get stack traces from perf going through ffi_call_unix64.

This is forward ported from gtk-3-24.

# Conflicts:
#	gtk/gtkeventcontrollerkey.c
#	gtk/gtkeventcontrollermotion.c
#	gtk/gtkgesture.c
#	gtk/gtkgesturemultipress.c