git: openjdk/jdk-sandbox: json: fix immutability in of() factories. Add immutability test to structural JSON

[duke]

Changeset: 49a130b7
Branch: json
Author:    Justin Lu <justin.lu at oracle.com>
Date:      2025-03-04 14:48:25 +0000
URL:       https://git.openjdk.org/jdk-sandbox/commit/49a130b77fa86d226da45aef8403b9e37f99a2b2

fix immutability in of() factories. Add immutability test to structural JSON

! src/java.base/share/classes/java/util/json/JsonArrayImpl.java
! src/java.base/share/classes/java/util/json/JsonObjectImpl.java
! test/jdk/java/util/json/TestJsonArray.java
! test/jdk/java/util/json/TestJsonObject.java