feat(VideoInfo): support get by endpoint + more info

[patrickkfkan]

Adds support for getting video info by endpoint in getInfo(). In addition, add playlist and autoplay to VideoInfo.

The result is that you can now obtain video info within the context of a list such as Playlist or Mix. To illustrate, consider the following endpoint for a Mix item:

// mixEndpoint:
{
  "type": "NavigationEndpoint",
  "payload": {
    "videoId": "XHedu3KcPP0",
    "playlistId": "RDXHedu3KcPP0",
    "params": "OALAAQE%3D",
    "continuePlayback": true
  },
  ...
}

// Call `getInfo()` with mixEndpoint:

const info = await youtube.getInfo(mixEndpoint);

// Now you can get not only info about the video (as referenced by id 'XHedu3KcPP0') itself, but 
// also other items in the list.

// info.playlist:
{
  "id": "RDXHedu3KcPP0",
  "title": "Mix - ...",
  "author": ...,
  "contents": [
    {
      "type": "PlaylistPanelVideo",
      ...
    }
  ]
  ...
}

info.playlist mirrors what you would see on YouTube:

Now, say you want to play the last item in the list and get info on that:

const lastVideo = info.playlist.contents.pop();
const newInfo = await youtube.getInfo(lastVideo.endpoint);

// `newInfo.playlist` will now have updated contents based on the `selected` video.
// In the context of a Mix, there would be new items added with some older ones removed.

In addition, you can get the Autoplay video endpoint:

const endpoint = info.autoplay_video_endpoint;

// or obtain from `info.autoplay`

This points to the next item in the list or, if there are none (end of list reached), a video as determined by YouTube autoplay logic.

Of course, you can still call getInfo() with video_id: string. Apparently, there won't be playlist info in this case.