[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 58 am: 07cd4ca6 -s ours am: 9c52a97e -s ours am: 51b3cfa8 -s ours am: 1d131eda -s ours am: 71fba886 am: 39b1d9a6 Change-Id: Ia056535d87d1084f6162ce469ce3d1f0b9fb7ad0