[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4J 58 am: fc5a01ba3d -s ours am: 8eb668d374 -s ours am: 3f055f5bde -s ours am: 43be8bba2a -s ours
am: 29967cf6f2

Change-Id: Ica4d9fa7fe7c42806ca56eea554f55496e37d2b6