This new element wraps both the base H264 decoder and lcevcdec elements into a
bin so that LCEVC decoding works with auto-plugging elements such as decodebin.
By default, the H264 decoder element with higher rank is used as base decoder,
but any particular H264 decoder can be used by manually setting the base-decoder
property.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7330>
