Japanese new era implementation

It is anticipated that the announcement of the name of the new era may not be ready for the last JDK update before the beginning of the new era (May 1st, 2019).
In order to make it a smooth transition, implement the new era with a placeholder name "NewEra" (default) and 新元号 (in Japanese), so that the "year of era" value should be correctly calculated. The placeholder should be replaced with the genuine name after it is announced (with JDK-8174268)