Drop jQuery and UnderscoreJS

[pradyunsg]

Toward #7405

• Port doctools.js
  • (missing piece right now is make the search highlighting work)
  • Update tests
• Port searchtools.js
  • Update tests
• Documentation callouts
• Changelog entry

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Live-ish list of changes:

• Make all JS function utilities "private", by prefixing an underscore.
• When highlighting content, only highlight content within [role="main"],
  since that is where the search is done.
• Only handle toggle buttons for domainindex.js, in [role="main"].
• Drop unused JS functions: addContextElements, getCurrentURL, makeURL.

[AA-Turner]

@pradyunsg can this be closed since #10028 was merged?

A

[pradyunsg]

Yes!