fix(cssxref): Correct fit-content() slug and calc() example anchor

[dipikabh]

Description

This PR fixes the following:

• Updates fit_content_function to fit-content_function to match the file slug in fit-content().
• Includes the anchor fragment in the example that shows how to use the 3rd parameter of the macro.

Motivation

The incorrect fit_content_function mapping will not work for {{cssxref("fit-content()")}}

[github-actions]

b233a54 was deployed to: https://rari-pr431.review.mdn.allizom.net/

[dipikabh]

While we're here, could we also get special handling for these two items that are both in /Web/CSS/Reference/Values:

• "&lt;url&gt;" | "<url>" => "url_value" (https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/url_value)
• "url()" => "url_function" (https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/url_function)