[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 58 am: fc5a01ba3d -s ours am: 8eb668d374 -s ours
am: 29b114fbae -s ours
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Change-Id: Iac2f3b81d0b7047555f859080f8ecf848b1ac991