chore: add back _client method (#10910)

packages/puppeteer-core/src/common/Frame.ts

@@ -72,6 +72,15 @@ export class CdpFrame extends Frame {
     });
   }
 
+  /**
+   * This is used internally in DevTools.
+   *
+   * @internal
+   */
+  _client(): CDPSession {
+    return this.#client;
+  }
+
   /**
    * Updates the frame ID with the new ID. This happens when the main frame is
    * replaced by a different frame.