Description:
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mb_convert_kana() does not convert japanese iteration marks (odori-ji).

* Hiragana to Katakana ($option = 'C')
ゝ and ゞ must be converted ヽ and ヾ

* Katakana to Hiragana ($option = 'c')
ヽ and ヾ must be converted ゝ and ゞ


Test script:
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<?php
echo mb_convert_kana('あゝすゞめアヽスヾメ', 'C', 'UTF-8') . PHP_EOL;
echo mb_convert_kana('あゝすゞめアヽスヾメ', 'c', 'UTF-8') . PHP_EOL;


Expected result:
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アヽスヾメアヽスヾメ
あゝすゞめあゝすゞめ

Actual result:
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アゝスゞメアヽスヾメ
あゝすゞめあヽすヾめ