[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 58 am: 07cd4ca63c -s ours am: 9c52a97ef0 -s ours
am: 51b3cfa897 -s ours
am skip reason: subject contains skip directive

Change-Id: Ia2ed84cb58749221379d002b3846ced23342efe6