rename beak_mask -> bird_mask

BUR #6732 has been approved by @nonamethanks.

rename beak_mask -> bird_mask
create implication bird_mask -> mask

Most of beak mask is a single arknight character.
Rename instead of alias so it's not confused for plague doctor mask.

Should fake_beak also be included?

Moved manually to beak mask for now.

The bulk update request #6732 (forum #194265) has been approved by @nonamethanks.