Clarify exception message for repeated builders.

Technically these methods fail either if the field is primitive (non-message) or if the field is repeated.  However it is confusing to have a repeated message field  claim to be of type 'message' and then fail with an error message that claims you need a message type.

PiperOrigin-RevId: 693789370

csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs

@@ -1,17 +0,0 @@
-#region Copyright notice and license
-// Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.  All rights reserved.
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
-#endregion
-
-namespace Google.Protobuf.Reflection;
-
-internal sealed partial class FeatureSetDescriptor
-{
-    // Canonical serialized form of the edition defaults, generated by embed_edition_defaults.
-    private const string DefaultsBase64 =
-        "ChMYhAciACoMCAEQAhgCIAMoATACChMY5wciACoMCAIQARgBIAIoATABChMY6AciDAgBEAEYASACKAEwASoAIOYHKOgH";
-}

java/core/src/main/java/com/google/protobuf/GeneratedMessage.java

@@ -2709,13 +2709,12 @@ public abstract class GeneratedMessage extends AbstractMessage implements Serial
 
       @Override
       public Message.Builder newBuilder() {
-        throw new UnsupportedOperationException(
+        throw new UnsupportedOperationException("newBuilderForField() called on a repeated field.");
-            "newBuilderForField() called on a non-Message type.");
       }
 
       @Override
       public Message.Builder getBuilder(GeneratedMessage.Builder<?> builder) {
-        throw new UnsupportedOperationException("getFieldBuilder() called on a non-Message type.");
+        throw new UnsupportedOperationException("getFieldBuilder() called on a repeated field.");
       }
 
       @Override