[GlobalPlayer,Whyp,DLF, Clipchamp] Add new extractors back-ported from yt-dlp

[dirkf]

Boilerplate: yt-dlp code, new extractor+improvement

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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 adds four new extractors back-ported from yt-dlp, together with some core improvements to support them.

• GlobalPlayer, from [extractors/globalplayer] add Global Player extractors yt-dlp/yt-dlp#6903, thanks @garret1317; resolves GlobalPlayer #31688
• Whyp, from [extractor/whyp] Add extractor yt-dlp/yt-dlp#6803, thanks @CoryTibbettsDev
• DLF, from [extractor/dlf] Add support for Deutschlandfunk yt-dlp/yt-dlp#6697, thanks @nick-cd
• Clipchamp, from [extractor/clipchamp] Add extractor yt-dlp/yt-dlp#6978, thanks @bashonly.

Supporting improvements:

• update traverse_obj() to support traversal of Iterables, sets and re.Matches (aka compat_re_Match): thanks @Grub4K; add convenience function T() as a (slight) abbreviation of set((x,)) since literal set {x} isn't in Py2.6
• improve js_to_json(): thanks @ChillingPepper, @Grub4K, @pukkandan; add limited support for ! evaluation (eg, !!0 -> false)
• support multiple groups in group argument of InfoExtractor._search_regex()`, etc
• add keyword arguments to merge_dicts(): unblank=True to disallow empty string, rev=False to reverse the order of merge_dict's args list; rev=True matches {**dict1, **dict2, ...} (not in Py 2)
• add search methods for Next/Nuxt.js from yt-dlp to InfoExtractor with tests
  • _search_nextjs_data(), from haruhi-dl backporting, batch 1 yt-dlp/yt-dlp#1386
    thanks @selfisekai
  • _search_nuxt_data(), from [extractor/common] introduce _search_nuxt_data yt-dlp/yt-dlp#1921,
    thanks @Lesmiscore, @pukkandan
• fix HTML5 type recognition and tests, from yt-dlp/yt-dlp@222a230, thanks @Lesmiscore
• add _match_valid_url() class method to InfoExtractor and refactor
• support Sequence of patterns in _VALID_URL.

An immediate compat fix to traverse_obj() is also included: fixes #32456.