8241311: Move some charset mapping tests from closed to open

Reviewed-by: iris, joehw, itakiguchi, amlu

Author: naotoj

test/jdk/sun/nio/cs/TestCharsetMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -24,6 +24,7 @@
 /* @test
  * @bug 8186801 8186751
  * @summary Test the charset mappings
+ * @modules jdk.charsets
  */
 
 import java.io.*;