[CSS] Update animation-timeline property for Anonymous Scroll Progress Timelines

[Rumyra]

Acceptance Criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• 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
  or
• Add entry to Firefox experimental features page if feature is not yet enabled in release

Features to document

Update animation-timeline property for Anonymous Scroll Progress Timelines

Related Gecko bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1737918

[Rumyra]

Status

• scroll() function page - Anonymous scroll timelines #21707
• animation-timeline page update Anonymous scroll timelines #21707
• CSS function page update Anonymous scroll timelines #21707
• css data - animation-timeline - add scroll syntaxes data#621
• BCD - FF101 CSS scroll() function on animation_timeline browser-compat-data#18064
• rel notes - NA - this is behind pref -
• Using CSS Animations - choose NOT to update - until this is shipped somewhere.

I think all the work needed for this has been done except for reviews.

[Rumyra]

This is the bug for this feature https://bugzilla.mozilla.org/show_bug.cgi?id=1733260 it would be best to wait for dependancies to be implemented before documenting - I'm closing this issue and will re-open once this lands

[hamishwillee]

This can now be documented (though it is behind pref) based on this comment from a couple of weeks ago in but 1733260 here:

Let's document this, per https://drafts.csswg.org/scroll-animations-1/#scroll-timelines. it is the combination of Bug 1737918 and Bug 1754897.

The first part is about anonymous timelines being created using the scroll() function - i.e. this bug. I did the other part on named timelines in #21069

@Rumyra Do you want me to take this. I'm somewhat on top of this.

[Rumyra]

Yes absolutely @hamishwillee - I'm hoping this work can help us decide what to do with this page https://developer.mozilla.org/en-US/docs/Web/CSS/@scroll-timeline - it came in and out pretty quickly so I think it can be removed as long as there's a good redirect

[hamishwillee]

I'm hoping this work can help us decide what to do with this page https://developer.mozilla.org/en-US/docs/Web/CSS/@scroll-timeline - it came in and out pretty quickly so I think it can be removed as long as there's a good redirect

Deleted and redirectd in #21704 . Not needed and can only be potentially confusing at this point.

[hamishwillee]

Pretty much done, as per #15467 (comment). Just waiting on all the reviews to be done.

Note, when this ships we should also update Using CSS Animations. This should be easy enough using the examples we have created here. Just think it is a bit early now.