[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 58 am: 07cd4ca63c -s ours am: 33dc1eb961 am: 057adef1be am: c1c5c82fd5 -s ours am: 71b3f220b6 -s ours
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Change-Id: Ib1cc6c101cadf5b1598de8dad804458d58d17180