[YouTube] Add support for extracting auto-translated captions

[TobiGr]

• 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.

Extract auto-translated captions for YouTube videos.

API changes 🟢

SubtitlesStream

This adds isAutoTranslated() next to isAutoGenerated() to distinguish between auto-generated subtitles which use speech2text and auto-translated captions based on Google translator.
Additionally, getBaseLocale(), getDisplayBaseLanguageName() and getBaseLanguageTag() were added to access info on the language which was used for auto-translations.

Issues closed by this PR

Closes #977
Based on and adresses TeamNewPipe/NewPipe#8023

[AudricV]

I would not base the extraction on the index, but rather on whether the subtitles are auto-generated:

Suggested change

	if (i == 0 && caption.getBoolean("isTranslatable")
	if (isAutoGenerated && caption.getBoolean("isTranslatable")

Also, this PR doesn't add support of subtitles translation for uploaded subtitles. For instance, see https://www.youtube.com/watch?v=_cMxraX_5RE: you can translate from German to French and from English to French, and the translations are different.

We may need another property in SubtitlesStream for this.

[TobiGr]

I don't understand why we should use isAutoGenerated here. For better quality, it should be !isAutoGenerated. Manually added captions should be exact.
I was also wondering whether we should provide the auto-translated captions by default. Extracting the data for and generating ~100 SubtitleStreams takes some time. I'd definitely not recommend to do this for all available languages by default. On the other hand, we could provide a method which does this when needed.

[TobiGr]

I decided to extract all available subtitles, but made sure to speed up the process. It's up to the frontends to filter the subtitles.

[Facni]

What happened to this?

[Stypox]

Is something blocking this PR from getting merged (except the needed rebase)? @AudricV

(some user asked via email about this feature)