Resolve the nit-picky reference warnings in Doc/library/http.cookiejar.rst
and drop the file from Doc/tools/.nitignore so future regressions are
caught by CI.

Documented targets are qualified with their owning class, for example
Cookie.version, CookiePolicy.rfc2965, the urllib.request.Request methods
and attributes, and urllib.response.addinfourl.info. References with no
documented target become inline literals: the removed get_origin_req_host
method.

The http.server part of the issue is left for a separate change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…ge, markup

Apply Hugo's review feedback for Doc/library/http.cookiejar.rst:

- Use sentence case for the four "... Objects" section headers.
- Replace the Latin abbreviations "ie."/"eg." with "that is"/"for
  example" per the devguide simple-language guidance.
- Use ``None`` literal markup instead of :const:`None`.
- Reference the removed method as :meth:`!get_origin_req_host` to match
  the surrounding formatting.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…self.filename

Apply Stan's review feedback:

- Point the response info() reference at http.client.HTTPResponse rather
  than the deprecated urllib.response.addinfourl.info.
- Keep the FileCookieJar.save attribute references as self.filename so
  they read clearly, using :attr:`!self.filename` to avoid a broken
  cross-reference.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Per Stan's suggestion, use the explicit-title cross-reference
:attr:`self.filename <FileCookieJar.filename>` so the text still reads
"self.filename" while linking to the documented attribute.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>