fix(Parser): Add UpdateEngagementPanelContentCommand

This command is sometimes used to open the Transcript panel.

src/parser/classes/commands/UpdateEngagementPanelContentCommand.ts

@@ -0,0 +1,20 @@
+import { YTNode } from '../../helpers.js';
+import { type RawNode } from '../../index.js';
+
+type Identifier = {
+  surface: string,
+  tag: string;
+}
+
+export default class UpdateEngagementPanelContentCommand extends YTNode {
+  static type = 'UpdateEngagementPanelContentCommand';
+
+  public content_source_panel_identifier?: Identifier;
+  public target_panel_identifier?: Identifier;
+  
+  constructor(data: RawNode) {
+    super();
+    this.content_source_panel_identifier = data.contentSourcePanelIdentifier;
+    this.target_panel_identifier = data.targetPanelIdentifier;
+  }
+}