fix(docs): Improve fit-content and other sizing keyword pages

[dipikabh]

Description

A user on Discord reported that the description for fit-content was misleading and unclear.

I also found that the reference to fit-content(stretch) is outdated and should be removed.
From CSS Box Sizing Level 3 spec:
> Note: This section previously defined stretch and fit-content as keywords representing the stretch-fit size and fit-content size, respectively. These keywords have been deferred to Level 4 (along with an additional contain keyword that behaves similarly to stretch but preserves the preferred aspect ratio, if any) to better work out the implications in situations with indefinite available space.

Updates in this PR

• Improved and clarified the description of fit-content.
  • Removed the outdated reference to fit-content(stretch). Updated the note.
  • Moved the formula to the "Description" section.
• Made the language and structure more consistent across other related sizing keyword pages: max-content and min-content.
• Made light edits to the related glossary page for Intrinsic size.
  • Converted the subsection on "Extrinsic size" into a new glossary entry.

Motivation

To ensure content is accurate, up-to-date, and easier to understand

[github-actions]

Preview URLs (7 pages)

• /en-US/docs/Glossary/Extrinsic_size
• /en-US/docs/Glossary/Intrinsic_Size
• /en-US/docs/Web/CSS/CSS_box_sizing/Understanding_aspect-ratio
• /en-US/docs/Web/CSS/CSS_box_sizing
• /en-US/docs/Web/CSS/fit-content
• /en-US/docs/Web/CSS/max-content
• /en-US/docs/Web/CSS/min-content

External URLs (1)

URL: /en-US/docs/Glossary/Extrinsic_size
Title: Extrinsic size

• https://drafts.csswg.org/css-sizing-3/ (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2025-07-08 15:03:11)

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.