Improving ThePlatform Metadata extraction

[trainman261]

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Description of your pull request and other information

This improves metadata extraction for sites that use ThePlatform and updates the tests accordingly:

• "standard" metadata fields: tags/keywords and categories.
• A number of metadata fields have site-specific prefixes, but many of those metadata fields themselves are not site-specific (for instance creator, series, season number in this PR). I had started a discussion on this topic on Discord a while ago, but the discussion stalled IMO without a resolution. Consider this a proposal continuing the discussion that is open to changes. The proposed method could also help solve an issue in the NBC IE where it subclasses ThePlatformIE instead of subclassing InfoExtractor which AFAIK is not best practice (see the comment on line 32).

I have done the same level of regression testing as for my previous ThePlatformIE PR and have fixed all regression issues that appeared.

I am also now proposing to add the media_type field with this PR. This should be more carefully looked at, since I don't know much about the code outside of the extractor classes - I've tried to find where changes are needed but I only found the explanation in the common extractor class. Please add any other changes that may be necessary.

Fixes #

Template

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• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

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What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[bashonly]

And, unrelated to my review (out-of-scope for this PR):

The proposed method could also help solve an issue in the NBC IE where it subclasses ThePlatformIE instead of subclassing InfoExtractor

I am thinking these multi-purpose extractors such as ThePlatformIE and AnvatoIE etc should be refactored so that all of their useful methods are in a baseclass, and so that the many extractors improperly subclassing from concrete IEs can properly subclass from the refactored baseclasses instead

[trainman261]

I've implemented the suggested changes and made some slight changes to them.
I've also added the media_type field, however, I don't know what other code has to be updated to properly support this, so please add whatever is necessary - or let me know so I can update those parts myself. I've updated the description of the PR to match.

[seproDev]

I just noticed that the CWTVIE and AENetworksIE tests also needs to be updated

[trainman261]

@seproDev I've updated everything I can - unfortunately, those tests are either geo-restricted, subscriber-only or broken. If anyone has access they can feel free to add them.

[seproDev]

I've pushed those changes myself

[pukkandan]

Ignore the failing test. Pypy just randomly crashes sometimes

[trainman261]

I've merged everything together and addressed all the issues. Anything else?

@pukkandan I've noticed Pypy crashing on my system occasionally as well. Is there any pattern that could be reported as an error (to Pypy devs)?