Allowing better control over the way discovery happens and allowing
us to expose a proper API.
This also adds the potential of implementing more multi-threaded
discovery in a clean way in the future.
This allows us to cleanly expose the new
GstDiscoverer::load-serialize-info signal.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3911>
The previous code was storing container children in reverse
addition order, this was mitigated by the fact that track elements
were also stored in reverse order, thus restoring the original
order, but it seems more consistent to preserve order throughout,
the extra cost of append operations is negligible.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1549>
