Move nullability interceptor to end

Author: JordonPhillips

smithy-docgen-core/src/main/java/software/amazon/smithy/docgen/core/integrations/BuiltinsIntegration.java

@@ -51,8 +51,8 @@ public List<? extends CodeInterceptor<? extends CodeSection, DocWriter>> interce
             DocGenerationContext context) {
         return List.of(
                 new ErrorFaultInterceptor(),
-                new NullabilityInterceptor(),
-                new DefaultValueInterceptor()
+                new DefaultValueInterceptor(),
+                new NullabilityInterceptor() // This goes last so that its output is always first.
         );
     }
 }