[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 56 am: 1aa02d75f9 -s ours am: ceb8b7da47 am: 479c44f420 am: 1acd4f6978 -s ours am: 7aa59c8e72 -s ours
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Change-Id: Ibd9eb2dd2e7f3043c9fcfa62814d0269112b5fe4