[carousel] Implement scroll-markers property
The 'scroll-markers' property specifies whether the scroll container
should have a '::scroll-marker-group' pseudo element created, and its
position relative to the scroll container: none, before, after.
Bug: 332396355
Change-Id: I0abbdcfcfa55b9ca038c001a496e13aeddadea4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5527124
Reviewed-by: Rune Lillesveen futhark@chromium.org
Commit-Queue: Daniil Sakhapov sakhapov@chromium.org
Cr-Commit-Position: refs/heads/main@{#1300514}