Update the javadoc in the Character class to state support for GB 18030-2022 Implementation Level 2

Summary

Support "Implementation Level 2" of the GB18030-2022 standard

Problem

In order for middleware applications to support "Implementation Level 2" of the GB18030-2022 standard, Java SE has to support the level.

Solution

"Implementation Level 2" requires to support characters on 通用规范汉字表 (Tōngyòng Guīfàn Hànzìbiǎo; aka TGH 2013), which lists 8,105 ideographs. Those characters (code points) are all supported by Java SE 11 (with the fix to JDK-8301401), thus only the number of the implementation level in the Character class description needs to be updated.

Specification

Apply the following diff to java.lang.Character class description:

--- a/src/java.base/share/classes/java/lang/Character.java
+++ b/src/java.base/share/classes/java/lang/Character.java
@@ -55,7 +55,7 @@
  * of the Unicode Standard, with two extensions. First, the Java SE 11 Platform
  * allows an implementation of class {@code Character} to use the code points
  * in the range of {@code U+9FEB} to {@code U+9FEF} from the Unicode Standard
- * version 11.0, in order for the class to allow the "Implementation Level 1"
+ * version 11.0, in order for the class to allow the "Implementation Level 2"
  * of the Chinese GB18030-2022 standard. Second, the Java SE 11 Platform
  * allows an implementation of class {@code Character} to use the Japanese Era