MoltenVK requires VK_KHR_portability_enumeration and
VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR to surface
portability devices via enumeratePhysicalDevices. Without the flag
the adapter is hidden on some driver versions, causing
"Could not find suitable device" failures.
Add the instance extension and flag when available, and add
diagnostic logs for all MoltenVK fallbacks (depthClipEnable,
colorWriteEnable, depthBounds, fragmentShaderBarycentric)
so black-screen diagnostics are actionable.
On macOS the Vulkan loader comes from MoltenVK. SDL's default
probe only searches system paths, so a bundled libMoltenVK.dylib
next to the executable is invisible under the hardened runtime.
Probe it explicitly via SDL_GetBasePath() before falling back to
SDL's default search. Respect SDL_VULKAN_LIBRARY overrides and
log which loader is used. Update README to reflect that no
environment variable is required for bundled builds.
Co-Authored-By: internal-model
nacimoualla
