[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 58 am: 07cd4ca6 -s ours am: 33dc1eb9 am: 057adef1 am: c1c5c82f -s ours am: 71b3f220 -s ours am skip reason: subject contains skip directive Change-Id: I74d8363b9315397e7126f8af9b220bc0ad0b9ebe