[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 56 am: 18c03b9631 -s ours am skip reason: subject contains skip directive skipped: 384bda0e59

Change-Id: I7a6e4b412f46e99f893c4e9d86f46763deeecaf5