Add legacy signals connectAfter method
GObject signals have a connect_after function that we don't have in the gjs core signals, while it can be useful in some situations.
So introduce it.
(Follow up from !757 (merged))
GObject signals have a connect_after function that we don't have in the gjs core signals, while it can be useful in some situations.
So introduce it.
(Follow up from !757 (merged))