This introduce a common place for generic functions and factor out the plugin registration code. This code is nearly identical between implementation. Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1216>
This is derived from the H264 decoder, some boiler plate will be factored out in the following commits. Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1216>