HOTFIX: avoid breaking code that is created with "daml codegen" from older SDK but links against more recent java-bindings (#17648)

We provide a default implementation of `jsonEncoder` for `codegen.DefinedDataType`. This will fail if called, but older codegen will presumably not want to call `toJson` because it was not previously provided.

This is to unbreak the `canton` repo. See
https://app.circleci.com/pipelines/github/DACH-NY/canton/59000/workflows/58a9cfae-4e75-4062-b9c4-dbbf9544dc46/jobs/1576433/parallel-runs/0/steps/0-117

language-support/java/bindings/src/main/java/com/daml/ledger/javaapi/data/codegen/DefinedDataType.java

@@ -28,7 +28,16 @@ public interface DefinedDataType<T> {
   /** Produce the encoded form. */
   Value toValue();
 
-  JsonLfEncoder jsonEncoder();
+  // To avoid breaking code generated by old code-generators that link against updated java-bindings
+  // we provide a default implementation. Calling toJson will fail but old code-gen won't use it.
+  // TODO(raphael-speyer-da): Remove this once we can expect users of codegen to have caught up.
+  default JsonLfEncoder jsonEncoder() {
+    throw new UnsupportedOperationException(
+        "no jsonEncoder implementation was provided for "
+            + this.getClass()
+            + ". Does the SDK version you are using for codegen match your version of the"
+            + " java-bindings library?");
+  }
 
   default String toJson() {
     var w = new StringWriter();