Fix broken sidebar menu links

[krzysdz]

Fixes #2359

With this and #2324 (and #2356, which should not be necessary for this), lychee with --include-fragments (and excluded language versions other than English) reports 0 errors.

One broken menu item in 4.x:

• /en/4x/api/request#reqparamname: separated 4.x and 3.x cases, as 4.x allows a default value (at least according to docs content)

Broken menu items in 3.x:

• /en/3x/api/application#appallpath-callback--callback-: moved optional parameter to last pos to match 4.x and 5.x header
• /en/3x/api/application#applistenport-host-backlog-callback: separated 3.x from 4.x/5.x
• /en/3x/api/application#apprenderview-locals-callback: renamed options to locals (see 9162fa1)
• /en/3x/api/application#appusepath-callback--callback: separated 3.x from 4.x/5.x as according to API docs 3.x allows only one function per .use call
• /en/3x/api/request#reqheaderfield: merged with 4.x/5.x req.get() menu header, because it has been this way in old docs and I could not find req.header() outside req.get() description:
  

  expressjs.com/_includes/api/en/3x/req-header.md

  Lines 1 to 16 in 2d4df3f

  	<h3 id='req.get'>req.get(field)</h3>
  	Get the case-insensitive request header `field`. The "Referrer" and "Referer" fields are interchangeable.
  	```js
  	req.get('Content-Type')
  	// => "text/plain"
  	req.get('content-type')
  	// => "text/plain"
  	req.get('Something')
  	// => undefined
  	```
  	p Aliased as `req.header(field)`.

  
  

  expressjs.com/en/api/req-header.jade

  Lines 1 to 17 in 9e957d4

  	section
  	h3(id='req.get') req.get(field)
  	p
  	| Get the case-insensitive request header <code>field</code>.
  	| The <em>Referrer</em> and <em>Referer</em> fields are interchangeable.
  	+js.
  	req.get('Content-Type');
  	// => "text/plain"
  	req.get('content-type');
  	// => "text/plain"
  	req.get('Something');
  	// => undefined
  	p Aliased as <code>req.header(field)</code>.

• /en/3x/api/response#resclearcookiename--options: used header from 4.x/5.x (comma moved into [])
• /en/3x/api/response#rescookiename-value--options: used header from 4.x/5.x (comma moved into [])
• /en/3x/api/response#resdownloadpath--filename--options--fn: separated 3.x from 4.x/5.x, because signature is different
• /en/3x/api/response#resjsonbody: separated 3.x from 4.x/5.x, because 3.x allows optional status
• /en/3x/api/response#resjsonpbody: separated 3.x from 4.x/5.x, because 3.x allows optional status
• /en/3x/api/response#reslocationpath: renamed 3.x to match 4.x/5.x header
• /en/3x/api/response#resredirectstatus-path: renamed 3.x to match 4.x/5.x header and updated docs content to match (copied from 4.x)
• /en/3x/api/response#resrenderview--locals--callback: changed header to match 4.x (callback is optional); the 3.x docs are not great and somewhat differ from JSDoc
• /en/3x/api/response#ressendbody: separated 3.x from 4.x/5.x, because 3.x allows optional status
• /en/3x/api/response#ressetfield--value: used header from 4.x/5.x (comma moved into [])

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[krzysdz]

In the future we should somehow generate the menu based on the content, because doing it manually is very error-prone.