Self-cosplay aliasing

BUR #59188 has been approved by @evazion.

create alias midform -> self_cosplay

This is something I have been wanting to do, for a while now. I am aliasing the term for half-transformed magical girls, which is "midform", to the "self cosplay" tag.

The bulk update request #59188 (forum #438596) has been approved by @evazion.