Make it clear what arguments req.accepts* functions accept - #7452

TL;DR req.acceptsCharsets JSDoc comment claimed support for something that has not been supported since Express 4 and an LLM (user?) tried to "fix" it in code.

Description

req.accepts, req.acceptsEncodings, req.acceptsCharsets, req.acceptsLanguages are almost identical so I tried to:

• make the JSDoc comments consistent,
  • mention all possible argument types:
    • single string (returns false or the string),
    • multiple string arguments (returns false or the best/preferred),
    • an array of strings (returns false or the best/preferred),
    • no arguments (returns an array of supported thing sorted by preference);
  • add examples showing most of the above cases (argument types, return values),
  • add overloads that better reflect the behaviour (thought that it may help, but now I have doubts about this);
• change the methods to the same code style (based on Refactor: simplify acceptsLanguages implementation using spread operator #6137),
• test the things the new docs claim are supported.

Problems and things to discuss

1. The overloads probably are not necessary (the text content explains everything and the DefinitelyTyped types contain better docs/types). I would like to hear someone's opinion on this.
2. Code style and docs format were my arbitrary choice and probably could be better.
3. The tests are still a chaos (different structure in every file), but I don't plan to change this.
4. 2 tests fail, because I have written them based on RFC 9110 and the behaviour of negotiator/accepts/express when Accept-Encoding is missing does not match my interpretation of the standard - No Accept-Encoding defaults to only 'identity' jshttp/accepts#82
5. One test deletes a header, because of a problem with superagent - [fix] Cannot unset Accept-Encoding forwardemail/superagent#1860
6. req.acceptsCharsets now contains a note that the Accept-Charset header is deprecated - is it something that should be included in the docs?

If this is merged, the docs on the website should be updated too. On the website only req.acceptsLanguages() has String[] in return types.

TODO:

• Check whether @param {...string} name works with TS (...string[] that I use now I think is incorrect JSDoc)

Closes #7470