Fold ExactFieldName into FieldName (#106867)

FieldName does not make much sense as an abstract class with a single private subclass.
Also, the base implementation holds most of the fields that the subclass relies on to do its job.
They can be unified into a single class

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/support/SecurityIndexFieldNameTranslator.java

@@ -42,43 +42,31 @@ public class SecurityIndexFieldNameTranslator {
     }
 
     public static FieldName exact(String name, Function<String, String> translation) {
-        return new SecurityIndexFieldNameTranslator.ExactFieldName(name, translation);
+        return new SecurityIndexFieldNameTranslator.FieldName(name, translation);
     }
 
-    public abstract static class FieldName {
+    public static class FieldName {
+        private final String name;
         private final Function<String, String> toIndexFieldName;
         protected final Predicate<String> validIndexNamePredicate;
 
-        FieldName(Function<String, String> toIndexFieldName, Predicate<String> validIndexNamePredicate) {
+        private FieldName(String name, Function<String, String> toIndexFieldName) {
+            this.name = name;
             this.toIndexFieldName = toIndexFieldName;
-            this.validIndexNamePredicate = validIndexNamePredicate;
-        }
-
-        public abstract boolean supportsQueryName(String queryFieldName);
-
-        public abstract boolean supportsIndexName(String indexFieldName);
+            this.validIndexNamePredicate = fieldName -> toIndexFieldName.apply(name).equals(fieldName);
 
-        public String indexFieldName(String queryFieldName) {
-            return toIndexFieldName.apply(queryFieldName);
         }
-    }
 
-    private static class ExactFieldName extends FieldName {
-        private final String name;
-
-        private ExactFieldName(String name, Function<String, String> toIndexFieldName) {
-            super(toIndexFieldName, fieldName -> toIndexFieldName.apply(name).equals(fieldName));
-            this.name = name;
-        }
-
-        @Override
         public boolean supportsQueryName(String queryFieldName) {
             return queryFieldName.equals(name);
         }
 
-        @Override
         public boolean supportsIndexName(String indexFieldName) {
             return validIndexNamePredicate.test(indexFieldName);
         }
+
+        public String indexFieldName(String queryFieldName) {
+            return toIndexFieldName.apply(queryFieldName);
+        }
     }
 }