[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 58 am: fc5a01ba3d -s ours am: f04b16ccf8
am: e5e23d04ec

Change-Id: I1a25046dd291c0a41f4089cff2bce11a1721b1d5