add missing comments

Signed-off-by: Lukas Jungmann <lukas.jungmann@oracle.com>

Author: lukasj

api/src/main/java/jakarta/json/Json.java

@@ -58,6 +58,9 @@
  */
 public final class Json {
 
+    /**
+     * No instantiation.
+     */
     private Json() {
     }
 

api/src/main/java/jakarta/json/JsonPatch.java

@@ -85,8 +85,13 @@ enum Operation {
          */
         TEST("test");
 
+        /** Operation name */
         private final String operationName;
 
+        /**
+         * Create an enum constant with given {@code operationName}.
+         * @param operationName the operation name for the enum constant
+         */
         private Operation(String operationName) {
             this.operationName = operationName;
         }

api/src/main/java/jakarta/json/stream/JsonCollectors.java

@@ -40,6 +40,9 @@
 
 public final class JsonCollectors {
 
+    /**
+     * No instantiation.
+     */
     private JsonCollectors() {
     }