Invidious support

[B0pol]

• I carefully read the contribution guidelines and agree to them.
• I have tested the API against NewPipe.
• I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

TODO

• implement InvidiousChannelExtractor
• implement InvidiousChannelInfoItemExtractor
• implement InvidiousCommentsExtractor
• implement InvidiousCommentsInfoItemExtractor
• implement InvidiousFeedExtractor
• implement InvidiousStreamInfoItemExtractor
• implement InvidiousPlaylistExtractor
• implement InvidiousPlaylistInfoItemExtractor
• implement InvidiousSearchExtractor
• implement InvidiousSuggestionExtractor
• implement InvidiousTrendingExtractor
• add tests in NewPipeTest.java for Invidious (it will partially fix NewPipeTest.java only test YouTube #347)
• handle when instance is semi-blocked: i.e. when video is available but metadata are missing, e.g.
  
• add tests
• test in NewPipe
• next page logic when there is no continuation field but a page url parameter.
• mix extractor?

what can't be done:

• MusicSearchExtractor

maybe:

• search filters? the api provides

sort_by: "relevance", "rating", "upload_date", "view_count"
date: "hour", "today", "week", "month", "year"
duration: "short", "long"
type: "video", "playlist", "channel", "all", (default: video)
features: "hd", "subtitles", "creative_commons", "3d", "live", "purchased", "4k", "360", "location", "hdr" (comma separated: e.g. "&features=hd,subtitles,3d,live")
region: ISO 3166 country code (default: "US")

currently we only sort by "type". IMO it shouldn't be in this PR, but in a separate one fixing #106 (and that will do for YouTube, Invidious, maybe PeerTube because the issue isn't about PeerTube but it's related).

You can push to the invidious branch if you want, but please announce you are working on invidiousXextractor before so that we are not two people wasting time on the same extractor.

• implement metaInfo, streamSegments?

[obeho]

Is this PR still under active development?

Btw, thanks for v0.20.1.