alias staff_(music) -> musical_staff

BUR #35961 has been approved by @evazion.

create alias staff_(music) -> musical_staff

Having this be a qualified tag really looks quite silly, especially when compared with musical staff print and musical note. This was aliased in topic #9998 (11 years ago!) on the basis of tag age, but I don't think that's a good reason to keep a clunky tag name.

The bulk update request #35961 (forum #332329) has been approved by @evazion.

Apparently sheet music is supposed to be for music scores written down on paper, while musical staff is supposed to be for music scores flying through the air and the like. We may still need a better name for this.