Re-add ModelUtils removed by a recent master commit

Author: Slavek Kabrda

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java

@@ -25,6 +25,7 @@
 import org.openapitools.codegen.languages.features.PerformBeanValidationFeatures;
 import org.openapitools.codegen.meta.features.DocumentationFeature;
 import org.openapitools.codegen.templating.mustache.CaseFormatLambda;
+import org.openapitools.codegen.utils.ModelUtils;
 import org.openapitools.codegen.utils.ProcessUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;