[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 60 am: a83e435ffa -s ours am: aa322e9e08 -s ours
am: ac625a3cbf

Change-Id: I5f9febcb0b3b4cbc6565e8d8ee831b01e0827a8a