Improvements to packing efficiency and updating UV packing API. * Add #pack_islands_alpaca_rotate, the fast alpaca-style packer with rotation. * Update heuristic for sorting islands based on longest edge. (Improves pack efficiency when rotation is enabled.) * Add `aspect_y` to UV Packing API, to support non-square materials in the future. Pull Request: https://projects.blender.org/blender/blender/pulls/105977