[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 56 am: 1aa02d75f9 -s ours am: 220221d43d -s ours am skip reason: subject contains skip directive skipped: d629acccbf

Change-Id: I7cac315a14070a9e54f6e2d72b54742477c745c8