Add class prefix to tag with numbers (#6561)

* add class prefix to tag with numbers, update java to default tag name

* update codegen test

modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultCodegen.java

@@ -3502,7 +3502,7 @@ public class DefaultCodegen {
 
         // tag starts with numbers
         if (tag.matches("^\\d.*")) {
-            tag = "_" + tag;
+            tag = "Class" + tag;
         }
 
         return tag;

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractJavaCodegen.java

@@ -1229,11 +1229,6 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
         additionalProperties.put(propertyKey, value);
     }
 
-    @Override
-    public String sanitizeTag(String tag) {
-        return camelize(sanitizeName(tag));
-    }
-
     /**
      * Output the Getter name for boolean property, e.g. isActive
      *