parse: Don't do delayed property setting for top-level properties.

parse: Don't do delayed property setting for top-level properties.

If a property is supplied to gst-launch-1.0 to set on a property that
implements GstChildProxy, it would always accept any property name
and try to set it later. This means that (for example) decodebin
will accept and not complain about property names that can never exist like:

gst-launch-1.0 videotestsrc ! decodebin NON-EXISTING_PROPERTY=adsfdasf ! fakesink

Instead, only try to do deferred property setting for property names
that contain the :: separator that indicates it's a setting on a child
that might appear later.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/832>