[automerger skipped] DO NOT MERGE Cherry-pick: ICU-20536 Japanese era Reiwa support in ICU4C 58 am: 07cd4ca63c -s ours am: 9c52a97ef0 -s ours
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am skip reason: subject contains skip directive

Change-Id: I5f35bcacaccd4e6741e91a74a02944e350120d6c