GROOVY-11905: Optimize non-capturing lambdas

Author: daniellansun

src/main/java/org/codehaus/groovy/ast/ClassNode.java

@@ -1452,17 +1452,21 @@ public ClassNode getOuterClass() {
         return null;
     }
 
+    private List<ClassNode> outerClasses;
     public List<ClassNode> getOuterClasses() {
+        List<ClassNode> ocs = outerClasses;
+        if (ocs != null) return ocs;
+
         ClassNode outer = getOuterClass();
         if (outer == null) {
-            return Collections.emptyList();
+            return outerClasses = Collections.emptyList();
         }
         List<ClassNode> result = new ArrayList<>(4);
         do {
             result.add(outer);
         } while ((outer = outer.getOuterClass()) != null);
 
-        return result;
+        return outerClasses = Collections.unmodifiableList(result);
     }
 
     /**