MoltenVK doesn't support a sampler mipLodBias (the portability subset's
samplerMipLodBias is false), so the PSP's LOD bias did nothing on Mac and
iOS, and biased textures came out a mip level blurrier than on OpenGL and
the PSP: MLB's signs and crowd, Burnout Legends, MediEvil, Ridge Racer 2.
Query the portability subset, and where the bias is missing, pass the auto
mode bias to texture() from a uniform instead.
VK_ENABLE_BETA_EXTENSIONS, which declares the portability subset, is now
defined for App Store iOS builds too.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
