Runs the same compute shaders as the Vulkan backend, translated to MSL,
in the upload command buffer: levels decode unscaled into the push
buffer and get scaled into a view of the level. Push constants go in a
buffer of their own. Multipass shaders (NNEDI3) use scratch textures
that live for the frame.
Shaders with a constant buffer (only the smiley test shader) aren't
supported.
All the texture shaders give the same result as Vulkan's on LocoRoco
and God of War savestates.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>