LibWeb: Add the HTMLOrSVGElement IDL interface mixin

Author: https://github.com/IdanHo
Commit: 1577bac6a5
Pull-request: https://github.com/SerenityOS/serenity/pull/13369
Reviewed-by: https://github.com/alimpfard ✅

Userland/Libraries/LibWeb/HTML/HTMLElement.idl

@@ -22,9 +22,6 @@ interface HTMLElement : Element {
     readonly attribute long offsetWidth;
     readonly attribute long offsetHeight;
 
-    // FIXME: This should come from a HTMLOrSVGElement mixin
-    [SameObject] readonly attribute DOMStringMap dataset;
-
     // FIXME: These should all come from a GlobalEventHandlers mixin
     attribute EventHandler onabort;
     attribute EventHandler onauxclick;
@@ -97,3 +94,9 @@ interface HTMLElement : Element {
     attribute EventHandler onwheel;
 
 };
+
+HTMLElement includes HTMLOrSVGElement;
+
+interface mixin HTMLOrSVGElement {
+    [SameObject] readonly attribute DOMStringMap dataset;
+};