uri-source: Respect stream-id even on streams muxed in raw

uri-source: Respect stream-id even on streams muxed in raw

The issue is that we rely on `decodebin::autoplug-select` to `SKIP`
unwanted pads, that signal was first provided to select factories during
autoplugin, not totally thought to avoid exposing pads. For streams
muxed directly in raw, decodebin has nothing to plug after the demuxer
and the pad is exposed right away, meaning that we do not have any
chance to avoid that pad to be exposed. This patch takes that limitation
into account and checks the stream ID of the pads exposed by decodebin
before exposing them itself, so we end up using the right pad even if
more are uselessly exposed by decodebin.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/issues/126

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/merge_requests/222>