[@Property] Support syntax
Spec: https://drafts.css-houdini.org/css-properties-values-api-1/#syntax-strings
Bug: 357751736
Change-Id: I61537a812b098bd5b336638653a254833828762d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5824390
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Commit-Queue: Munira Tursunova moonira@google.com
Cr-Commit-Position: refs/heads/main@{#1349162}