[extractor/facebook] Improve extraction

[dirkf]

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• Searched the bugtracker for similar pull requests
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• Read youtube-dl coding conventions and adjusted the code to meet them
• Covered the code with tests (note that PRs without tests will be REJECTED)
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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

This PR replaces #29796 which was orphaned when @kikuyan's account was deleted.

The PR makes the following fixes and improvements to the Facebook extractor:

• improves title, add description, preferring metadata in ld+json if present
• adds another getter for attachments (from PR [extractor/facebook] fix extraction #30496, issue)
• as ld+json VideoObject type seems to be gone since PR was first made, adds SocialMediaPosting type as a fallback
• when web pages are analyzed as playlists but consist of single video, treats the pages as regular video pages to extract metadata well (examples: tests 7, 9, 10)
• makes test skip for now: TestDownload.test_Facebook_8: the page cannot be parsed (get ERROR: This video is only available for registered users.) while it can be opened by a browser.

The PR makes the following improvement to the extractor/common.py:

• adds SocialMediaPosting for author extraction in InfoExtractor._json_ld() (replaces PR [extractor/common] add SocialMediaPosting type to _json_ld() #30513).

Resolves #29421, resolves #23627, resolves #23180, resolves #14156.
Resolves #30472, resolves #30474, resolves #30650, resolves #30681.

Closes #29796 (superseded)
Closes #30496 (superseded)
Closes #30513 (superseded).

[dirkf]

The extractor does this

            thumbnail = html_search_meta_non_empty(
                ['og:image', 'twitter:image'], webpage, 'thumbnail', default=None)

So it's looking for <meta (itemprop|name|property|id|http-equiv)=... content=...>

[ranelpadon]

Facebook video downloading has issue now which was already filed before in several related/duplicated issues:

ERROR: Cannot parse data

But it's working fine few days ago. Hopefully, this PR could be merged soon, since I badly needed the fix also. Thanks :)

[dirkf]

Are you saying that this happens with the PR code? Or (as I hope) that the PR code is still valid and fixes "Cannot parse data"?

That message basically means that the extractor tried all the tactics it knows to extract from the page and none worked.