Feat: Add support for replaying :defined pseudo-class of custom elements (#1155)

* Feat: Add support for replaying :defined pseudo-class of custom elements

* add isCustom flag to serialized elements

Applying Justin's review suggestion

* fix code lint error

* add custom element event

* fix: tests (#1348)

* Update packages/rrweb/src/record/observer.ts

* Update packages/rrweb/src/record/observer.ts

---------

Co-authored-by: Nafees Nehar <nafees87n@gmail.com>
Co-authored-by: Justin Halsall <Juice10@users.noreply.github.com>

packages/rrweb-snapshot/src/snapshot.ts

@@ -801,6 +801,13 @@ function serializeElementNode(
     delete attributes.src; // prevent auto loading
   }
 
+  let isCustomElement: true | undefined;
+  try {
+    if (customElements.get(tagName)) isCustomElement = true;
+  } catch (e) {
+    // In case old browsers don't support customElements
+  }
+
   return {
     type: NodeType.Element,
     tagName,
@@ -809,6 +816,7 @@ function serializeElementNode(
     isSVG: isSVGElement(n as Element) || undefined,
     needBlock,
     rootId,
+    isCustom: isCustomElement,
   };
 }