Support DASH SubRepresentation

[CastagnaIT]

Bug report

Describe the bug

Here is a clear and concise description of what the problem is:

The manifest of this stream make use of SubRepresentation fields that are not implemented in ISA,
then fallback on audio only

#KODIPROP:inputstream=inputstream.adaptive
#KODIPROP:inputstream.adaptive.manifest_type=mpd
#KODIPROP:inputstream.adaptive.stream_headers=User-Agent=RTP+Play%2F2.0.26+%28Linux%3BAndroid+11%29+ExoPlayerLib%2F2.11.8
https://streaming-ondemand.rtp.pt/nas2.share/h264/512x384/p9165/p9165_1_20210816161007e001t1185d/master.mpd?app

This is used on some RTPPlay streams
ref. @enen92 for RTPPlay addon

a future implementation will be required

MPD/M3U8s/ISM

An example or copy of a manifest (or manifests for HLS - master and variants) can be found here:
DashManifestSubRepresentation.txt

note: Once the issue is made we require you to update it with new information should that be required.
Team Kodi will consider your problem report however, we will not make any promises the problem will be solved.

[glennguy]

Very nice find!