LibWeb: Implement TransformStreamDefaultController::terminate()

Author: https://github.com/kennethmyhra
Commit: 4d4fc53f5c
Pull-request: https://github.com/SerenityOS/serenity/pull/19998
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/shannonbooth

Userland/Libraries/LibWeb/Streams/TransformStreamDefaultController.cpp

@@ -61,4 +61,13 @@ WebIDL::ExceptionOr<void> TransformStreamDefaultController::error(Optional<JS::V
     return {};
 }
 
+// https://streams.spec.whatwg.org/#ts-default-controller-terminate
+WebIDL::ExceptionOr<void> TransformStreamDefaultController::terminate()
+{
+    // 1. Perform ? TransformStreamDefaultControllerTerminate(this).
+    TRY(transform_stream_default_controller_terminate(*this));
+
+    return {};
+}
+
 }