[css-fonts] CSSFontFeatureValuesRule interface also moves to L4

Author: svgeesus

css-fonts-4/Overview.bs

@@ -3436,6 +3436,10 @@ The DOM Level 2 Style specification [[DOM-LEVEL-2-STYLE]]
 defined a different variant of this rule.
 This definition supercedes that one.
 
+<h3 id="om-fontfeaturevalues">
+The <code>CSSFontFeatureValuesRule</code> interface</h3>
+
+
 <h2 id="platform-props-to-css" class="no-num">
 Appendix A: Mapping platform font properties to CSS properties</h2>