Use new GStreamer elements

From https://gstreamer.freedesktop.org/releases/1.22/

Playbin3, Decodebin3, UriDecodebin3, Parsebin improvements

The "new" playback elements introduced in 1.18 (playbin3 and its various components) have been refactored to allow more use-cases and improve performance. They are no longer considered experimental, so applications using the legacy playback elements (playbin and (uri)decodebin) can migrate to the new components to benefit from these improvements.

Given v1.22 will soon be our min requirement, we can look at moving to these new elements.