[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: f75a37f4 -s ours am: 81637c54 -s ours am: 25de6c8b Change-Id: Ibe1774d6f02c323d788c1431a7b2698dfeae99f0