handle conflicting synthetic base exception name

Author: kuhe

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/PackageApiValidationGenerator.java

@@ -92,7 +92,8 @@ public void writeTypeIndexTest() {
                 }
 
                 // synthetic base exception
-                writer.write("$L,", aggregateClientName + "ServiceException");
+                String baseExceptionName = CodegenUtils.getSyntheticBaseExceptionName(aggregateClientName, model);
+                writer.write("$L,", baseExceptionName);
 
                 // waiters
                 closure.getWaiterNames().forEach(waiter -> {
@@ -169,7 +170,7 @@ public void writeRuntimeIndexTest() {
             );
         }
 
-        String baseExceptionName = aggregateClientName + "ServiceException";
+        String baseExceptionName = CodegenUtils.getSyntheticBaseExceptionName(aggregateClientName, model);
 
         // modeled errors and synthetic base error
         writer.write("// errors");