upb: implement .mergeFromBuffer() on GeneratedMessage in Dart

PiperOrigin-RevId: 628455567
diff --git a/conformance/conformance_dart.dart b/conformance/conformance_dart.dart
index 06b19b6..87d4359 100644
--- a/conformance/conformance_dart.dart
+++ b/conformance/conformance_dart.dart
@@ -65,7 +65,7 @@
   switch (request.requestedOutputFormat) {
     case WireFormat.PROTOBUF:
       try {
-        response.protobufPayload = pb.GeneratedMessage.toBuffer(testMessage);
+        response.protobufPayload = pb.GeneratedMessage.toBinary(testMessage);
       } catch (e) {
         response.serializeError = '$e';
       }
@@ -86,7 +86,7 @@
   }
   final request = ConformanceRequest.fromBuffer(serializedMsg);
   final response = doTest(request);
-  final serializedOutput = pb.GeneratedMessage.toBuffer(response);
+  final serializedOutput = pb.GeneratedMessage.toBinary(response);
   writeLittleEndianIntToStdout(serializedOutput.length);
   stdout.add(serializedOutput);
   await stdout.flush();