Support horizontal aspect ratio for flipbook animations

[Cubouse]

Detailed description of your suggestion

I was about to make a flipbook texture with a frame ratio of 2x1, went to duplicate the first frame, but ended up with a single frame. The canvas ratio was also bugged, so was painting and making selections.

https://github.com/user-attachments/assets/bbf4a79e-5e86-4aad-9a46-e5c4b8c50853