Add style container queries (web-platform-dx#577)

Author: foolip

feature-group-definitions/container-style-queries.yml

@@ -0,0 +1,6 @@
+name: Container style queries
+spec: https://drafts.csswg.org/css-contain-3/#style-container
+caniuse: css-container-queries-style
+usage_stats: https://chromestatus.com/metrics/feature/timeline/popularity/4550
+compat_features:
+  - css.at-rules.container.style_queries_for_custom_properties