[CSS] Add from-font keyword to font-size-adjust

[dipikabh]

Acceptance Criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• NA - Interactive example and data repos are updated if appropriate
• The content has been reviewed as needed

For folks helping with Firefox related documentation

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes if feature is enabled in release
• NA - Add entry to Firefox experimental features page if feature is not yet enabled in release

Features to document

Update https://developer.mozilla.org/en-US/docs/Web/CSS/font-size-adjust

Related Gecko bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1708240

Other

• Check content open issues to see if any pertain to the subject matter. If there are any that can be closed because of the work, do so. If there are any that can be fixed relatively quickly because of the knowledge from completing this issue and you have time, feel free to go ahead and fix them.
• Check if glossary updates are required for the feature you're documenting - whether an existing term needs to be updated or a new term should be added.
• Check if BCD update means that content pages need to have experimental markup removed or deprecated markup added (front matter tags and macros).

[dipikabh]

Tasks:

• Content page update: docs(css): Fx118 - Document new keyword "from-font" for the "font-size-adjust" property #29052
• Release note update: docs(relnotes): Fx118 - Add release note for "from-font" in CSS "font-size-adjust" #29058
• BCD update: Firefox 118 supports "from-font" keyword in CSS "font-size-adjust" property browser-compat-data#20693

"Formal syntax" on font-size-adjust content page is not in sync with the numbered spec version that's linked in the "Specifications" section on the content page. This is a known issue and being tracked here: #28900.