Add support for CSV+ZIP subscriptions (Google Takeout)

[talanc]

What is it?

• Bugfix (user facing)
• Feature (user facing)
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

Fixes #6757

Google Takeout now exports YouTube subscriptions as a CSV file (in a zip file).
This PR requires changes to NewPipeExtractor (now merged to dev).
It allows the user to select a CSV files for importing subscriptions.
If the user selects a ZIP file, it will go through the CSV files inside it and attempt to find the subscriptions file (the finding is a bit complicated due to different localizations).

Relies on the following changes

• [YouTube] Support csv and zip subscription import (Google Takeout)  NewPipeExtractor#709
• [YouTube] Small improvements to subscription import NewPipeExtractor#721

Due diligence

• I read the contribution guidelines.

[talanc]

I've updated the instructions in strings.xml as well.
I don't know if there's an additional localization process required.
Do I just delete the old translated strings because they're displaying the wrong information?

[TobiGr]

Please update the extractor version to your fork allowing the build to complete successfully and testers to check if everything works fine.

[talanc]

@TobiGr
I think it's done now...
If not I'll need a bit more guidance on what to do.

[Stypox]

Please rebase this and update the extractor commit, and it is ready.

[talanc]

@Stypox
All done.

[Stypox]

@talanc I added a commit to change the way the mime type is obtained. Your solution only worked when SAF was enabled, but would throw a NullPointerException with the old file picker. Is it ok? I also squashed your commits.

[TobiGr]

Thank you

[talanc]

@Stypox No problem. I was a bit unsure of that code. Thanks for improving it.

[Stypox]

Thank you @talanc :-D