utility alias double_peace -> double_v

BUR #11700 has been approved by @evazion.

create alias double_peace -> double_v

following peace_sign -> v, and this is the name pixiv uses: https://www.pixiv.net/en/tags/%E3%83%80%E3%83%96%E3%83%AB%E3%83%94%E3%83%BC%E3%82%B9/

The bulk update request #11700 (forum #218893) has been approved by @evazion.