Support for multiple face textures in one direction for block shapes

[Cervator]

Came up when discussing with Immortius recently, making issue as a reminder:

Block shapes that can apply different textures to the same face. Currently you're limited to using one texture per face (plus center) which prevents more complicated blocks (that perform better than full models) such as upholstered chairs.

That example could be using one texture for the seat cushion along with a wood-specific texture for the chair itself.

Low priority for now