2.0: Update the JVM's dependence on Unicode to 12.1

JVMS12 ch.2 refers to Unicode 11.0.0, but JVMS13 ch.2 should refer to Unicode 12.1 in accordance with the CSR JDK-8222771. (Since the thrust of ch.2 is that the JVM underlies the class libraries of the Java SE Platform, it is not desirable to follow JLS 3.1's style of deferring to java.lang.Character for the "current" version of Unicode supported by the JVM.)