support byte range for dash mpd

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Description of your pull request and other information

Add range and mediaRange attributes support of these types to dash mpd parser:

• segment URLs and range (resolves Video from MPEG-DASH stream much larger than same video from HLS stream #30235)
• no segment URLs but range (can supersede Ignore missing attributes in MPD manifests. #14648)

Also modified the existing code a bit at # Segment URLs with no SegmentTimeline in extractor/common.py for clarity, IMO.

Regarding the ftyp box

There seem to be some mpds that do not include ftyp box in the initialization segment because the range doesn't start from 0. As a result, the downloaded files do not have the box either. Such mpds are, for example, https://kinescope.io/200615537/master.mpd in #30235 and url_and_range.mpd made with Bento4 I added for test to this PR.
url_and_range.mpd has <Initialization sourceURL="video-frag.mp4" range="36-746"/>. If the source video file starts like

000000  0000 0024 6674 7970 6973 6f6d 0000 0200    ...$ftypisom....
000010  6973 6f6d 6973 6f32 6176 6331 6d70 3431    isomiso2avc1mp41
000020  6973 6f35 0000 02c7 6d6f 6f76 0000 006c    iso5....moov...l
000030  6d76 6864 0000 0000 ddc7 5e78 ddc7 5e78    mvhd......^x..^x

then the downloaded file will start like

000000  0000 02c7 6d6f 6f76 0000 006c 6d76 6864    ....moov...lmvhd
000010  0000 0000 ddc7 5e78 ddc7 5e78 0000 03e8    ......^x..^x....

This usually won't be a problem nor emerge because youtube-dl runs ffmpeg to merge video and audio, and the file will be adjusted. And for m4a_dash audio-only stream, fixup will be done.

While the video-only file seems to play fine with, say, VLC and QuickTime Player, I'm thinking of making another PR to run ffmpeg for fixup.