Call out 'bestvideo' and 'bestaudio' in -F output

[Siddhant]

• [x ] I've verified and I assure that I'm running youtube-dl 2019.03.18

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• [ x] At least skimmed through the README, most notably the FAQ and BUGS sections
• [ x] Searched the bugtracker for similar issues including closed ones
• [x ] Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

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• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• [ x] Feature request (request for a new functionality)
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C:\Users\Siddhant\Downloads>youtube-dl.exe -vF https://www.youtube.com/watch?v=LrCek73_e_M
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-vF', 'https://www.youtube.com/watch?v=LrCek73_e_M']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2019.03.18
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.17134
[debug] exe versions: ffmpeg 4.1, ffprobe 4.1
[debug] Proxy map: {}
[youtube] LrCek73_e_M: Downloading webpage
[youtube] LrCek73_e_M: Downloading video info webpage
[info] Available formats for LrCek73_e_M:
format code  extension  resolution note
249          webm       audio only DASH audio   60k , opus @ 50k, 4.85MiB
250          webm       audio only DASH audio   78k , opus @ 70k, 6.39MiB
140          m4a        audio only DASH audio  130k , m4a_dash container, mp4a.40.2@128k, 12.25MiB
171          webm       audio only DASH audio  137k , vorbis@128k, 12.09MiB
251          webm       audio only DASH audio  148k , opus @160k, 12.58MiB
394          mp4        256x144    144p   94k , av01.0.05M.08, 25fps, video only, 7.51MiB
278          webm       256x144    144p   98k , webm container, vp9, 25fps, video only, 8.80MiB
160          mp4        256x144    144p  112k , avc1.4d400c, 25fps, video only, 8.55MiB
395          mp4        426x240    240p  215k , av01.0.05M.08, 25fps, video only, 16.36MiB
242          webm       426x240    240p  226k , vp9, 25fps, video only, 19.15MiB
133          mp4        426x240    240p  247k , avc1.4d4015, 25fps, video only, 16.92MiB
396          mp4        640x360    360p  383k , av01.0.05M.08, 25fps, video only, 29.29MiB
243          webm       640x360    360p  418k , vp9, 25fps, video only, 35.02MiB
134          mp4        640x360    360p  635k , avc1.4d401e, 25fps, video only, 42.72MiB
397          mp4        854x480    480p  684k , av01.0.05M.08, 25fps, video only, 51.52MiB
244          webm       854x480    480p  769k , vp9, 25fps, video only, 62.69MiB
135          mp4        854x480    480p 1186k , avc1.4d401e, 25fps, video only, 81.86MiB
247          webm       1280x720   720p 1525k , vp9, 25fps, video only, 124.76MiB
136          mp4        1280x720   720p 2383k , avc1.4d401f, 25fps, video only, 151.93MiB
248          webm       1920x1080  1080p 2709k , vp9, 25fps, video only, 218.08MiB
137          mp4        1920x1080  1080p 4333k , avc1.640028, 25fps, video only, 265.88MiB
271          webm       2560x1440  1440p 8658k , vp9, 25fps, video only, 524.04MiB
313          webm       3840x2160  2160p 18393k , vp9, 25fps, video only, 1.36GiB
18           mp4        640x360    medium  697k , avc1.42001E, mp4a.40.2@ 96k (44100Hz), 65.96MiB (best)

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Description of your issue, suggested solution and other information

Just like format code '18' is called out as "(best)", can we also call out the "(bestvideo)" and "(bestaudio)"? In the above example, that would be format codes 313 and 251.
(Of course higher the size, higher the quality, so it's trivial for someone to determine which is the bestvideo and bestaudio. But is that correlation between size and quality always true? I don't know.)

I thought the simulate option -s would tell me which format it chooses when I ask for bestvideo+bestaudio, but surprisingly it did not:

C:\Users\Siddhant\Downloads>youtube-dl.exe -svf bestvideo+bestaudio https://www.youtube.com/watch?v=LrCek73_e_M
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-svf', 'bestvideo+bestaudio', 'https://www.youtube.com/watch?v=LrCek73_e_M']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2019.03.18
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.17134
[debug] exe versions: ffmpeg 4.1, ffprobe 4.1
[debug] Proxy map: {}
[youtube] LrCek73_e_M: Downloading webpage
[youtube] LrCek73_e_M: Downloading video info webpage