[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 56 am: 18c03b9631 -s ours am: a817b3cc9f am: 6acecc87a1 am: 468f5e6ba0 -s ours
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Change-Id: I5b33ea9e51afe5b4c0590c44165ebfe566c1a42f