Declare a public field for new Japanese Era Reiwa

Integrate OpenJDK commit for new Japanese Era name:

 * 8174268: Declare a public field in JapaneseEra for the era starting May 2019
   http://hg.openjdk.java.net/jdk/jdk/rev/6a4abdb6749c

Bug: 149437171
Test: CtsLibcoreTestCases CtsLibcoreOjTestCases
Change-Id: I3e84ed1d809376d2c646ceadc3421b5fb55982b5
6 files changed