*transcodebin: Port to encodebin2

commit 8b8fe2a2fa6550b4ef81bcdad5764e6280460e4a
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Fri Nov 20 11:29:46 2020 -0300

    transcodebin: Minor error message enhancement

commit 7ac219ad07a838efd37590f0befdbfd17fa9adb2
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 22:56:46 2020 -0300

    transcodebin: Unlock while setting decodebin caps
    
    Otherwise it will deadlock recursing up to notify parent object property changes

commit 052e00c30c655a5160979ebae0631b8a8371563b
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 18:31:34 2020 -0300

    transcodebin: Avoid plugin converter if filter handles ANY caps
    
    For example identity or clocksync or this kind of elements can be
    used with any data flow and we should not enforce decoding to row in
    that case.

commit eac98ea70e48375122009bc6d5af0d88f99e9e3d
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 18:39:33 2020 -0300

    transcodebin: Add filter as soon as it is set
    
    Instead of waiting so that we can simply use a clocksync element as
    filter, otherwise we won't know the pipeline is live as it won't
    return NO_PREROLL as one would expect in that case.
    
    Adding it right away shouldn't create any issue, both ways are fine.

commit 8f6989c69d9ed639446775ad58b392a41ab07a8f
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 18:29:15 2020 -0300

    uritranscodebin: Add `setup-source` and `element-setup` signals
    
    The same way as playbinX does it as it is often quite useful

commit a808e10c7ce0cace7171f0723822c9c7288f21fe
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 17:55:10 2020 -0300

    transcode: Port to encodebin2
    
    This allows supporting muxing sinks like hlssink2 or splitmux

commit 42dd8e4a67c572e4ce367dd7d1f857f109c9226b
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 17:55:10 2020 -0300

    transcoder: Handle the case where several errors are posted
    
    There were cases where the loop was already destroyed when we were
    receiving the following message.

commit 7131d937d625de31f6d97634f1d3b4384019f21b
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 17:54:28 2020 -0300

    transcoder: Minor refactoring to output better debug logs

commit 795eb8da52727d92914719279a06fca317e64467
Author: Thibault Saunier <tsaunier@igalia.com>
Date:   Thu Nov 19 17:51:56 2020 -0300

    hlssink2: Mark as Muxer
    
    The way it is usable by encodebin2. This is what splitmux does already.