Recognize gap as a css property. This prevents incorrect property renaming.

PiperOrigin-RevId: 707105983

Author: Closure Team

externs/browser/w3c_css.js

@@ -1433,6 +1433,12 @@ CSSProperties.prototype.fontVariant;
  */
 CSSProperties.prototype.fontWeight;
 
+/**
+ * @type {string}
+ * @see https://www.w3.org/TR/css-align-3/#propdef-gap
+ */
+CSSProperties.prototype.gap;
+
 /**
  * @type {string}
  * @see https://www.w3.org/TR/css-grid-1/#propdef-grid