[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: 14bece5cf5 -s ours am: 86fffc138a -s ours
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Change-Id: I1719a79d926e4aba17f2f2c93c625e2ca751f869