[BitChute] Back-port from yt-dlp and enhance

[dirkf]

Boilerplate: mixed code, improvement

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Before submitting a pull request make sure you have:

• Searched the bugtracker for similar pull requests
• Read adding new extractor tutorial
• 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)
• Checked the code with flake8

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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 re-works the BitChute extractor module based on the yt-dlp version, which in turn derives from the yt-dl version and unmerged yt-dl PRs.

The functional improvements are

• better extraction of videos (BitChuteIE)
• better extraction of channels (BitchuteChannelIE)
• added extraction of playlists (BitChutePlaylistIE)
• all tests pass.

Specific changes, apart from those needed for the yt-dl platform include the following.

Throughout

• relax regexes
• refactor common functions in BitChuteBaseIE, inherited by other IEs

BitChute

• extract timestamp instead of upload_date (resolves [bitchute] parse timestamp #24180, closes [bitchute] parse timestamp #24182)
• extract 'age_limit': 18 if NSFW
• better extraction of title and description
• detect 404 and report as expected error
• detected blocked channel and report as expected error (resolves Bitchute downloads not working #28461)
• extract channel_url (resolves channel_url for Bitchute #28500)

BitChuteChannel

• fix listing entries
• include NSFW if --age-limit 18 (or higher) (resolves Bitchute: Failure to report "NSFW" videos when listing a channel #24419)

BitChutePlaylist

• add extractor based on BitChuteChannelIE and PR [BitChutePlaylist] Add new extractor #26725 (resolves Add option to embed sub as synced lyrics tag. #29964, closes [BitChutePlaylist] Add new extractor #26725, would resolve [Bitchute] Playlist unrecognized yt-dlp/yt-dlp#2845)

Also closes #26569, resolves #29531.

Update: now resolves #32198.