[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 58 am: fc5a01ba3d -s ours am: f04b16ccf8 am: e5e23d04ec am: a837b28d8f -s ours am: be121509ba -s ours am: 6b171856dc
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Change-Id: I7d3d184682ff06931108f953e340ff5b818e3b79