[scroll-animations] Inset parameter of ViewTimelineOptions should be optional #11644
Description
Based on the test view-timelines/view-timeline-snapport.html, it is expected that ViewTimelines without a user specified timeline inset should avoid using the scroll-padding property as the inset. However, inset is defined as below in ViewTimelineOptions:
(DOMString or sequence<(CSSNumericValue or CSSKeywordValue)>) inset = "auto";
This definition doesn't make it possible to differentiate the user explicitly setting inset as auto vs the default value. My suggestion is to define it as an optional like below, so we can differentiate between these two cases:
(DOMString? or sequence<(CSSNumericValue or CSSKeywordValue)>) inset;