Add DiffEvaluator method that accepts ClassLoader

This adds a new, defaulted method to DiffEvaluator that additionally
takes a ClassLoader. This may be used for a number of reasons, but
was added particularly to allow running ModelDiff on synthetic
changes from an evaluator.

Author: JordonPhillips

.changes/next-release/feature-6d5a718d854e66c3e6b5d7dc2622a8d17e14f9b9.json

@@ -0,0 +1,7 @@
+{
+  "type": "feature",
+  "description": "Updated `DiffEvaluator` interface to include an optional method that additionally accepts a `ClassLoader`. This ensures that the loader the evaluation is configured with can be used in any evaluators that may need it.",
+  "pull_requests": [
+    "[#2796](https://github.com/smithy-lang/smithy/pull/2796)"
+  ]
+}

smithy-diff/src/main/java/software/amazon/smithy/diff/DiffEvaluator.java

@@ -29,4 +29,8 @@ public interface DiffEvaluator {
      * @return Returns validation events that are relative to the new model.
      */
     List<ValidationEvent> evaluate(Differences differences);
+
+    default List<ValidationEvent> evaluate(ClassLoader classLoader, Differences differences) {
+        return evaluate(differences);
+    }
 }