back_view -> from_behind utility alias

BUR #47363 has been approved by @evazion.

create alias back_view -> from_behind

back, the tag for someone's back, is routinely mistagged for from_behind; I've corrected a few hundred posts today already. Hopefully, this directs unknowing users to the correct tag.

This bulk update request is pending automatic rejection in 5 days.

This bulk update request has been rejected because it was not approved within 45 days.

The bulk update request #47363 (forum #386314) has been rejected by @DanbooruBot.

The bulk update request #47363 (forum #386314) has been approved by @evazion.