Vulkan: Support macOS via MoltenVK

The path to the MoltenVK library can be specified by the
LIBMOLTENVK_PATH environment variable, otherwise it assumes it is
located in the application bundle's Contents/MacOS directory.

Source/Core/VideoBackends/Vulkan/VulkanContext.cpp

@@ -186,6 +186,9 @@ bool VulkanContext::SelectInstanceExtensions(ExtensionList* extension_list, bool
 #elif defined(VK_USE_PLATFORM_ANDROID_KHR)
   if (enable_surface && !SupportsExtension(VK_KHR_ANDROID_SURFACE_EXTENSION_NAME, true))
     return false;
+#elif defined(VK_USE_PLATFORM_MACOS_MVK)
+  if (enable_surface && !SupportsExtension(VK_MVK_MACOS_SURFACE_EXTENSION_NAME, true))
+    return false;
 #endif
 
   // VK_EXT_debug_report
@@ -833,6 +836,13 @@ void VulkanContext::InitDriverDetails()
     driver = DriverDetails::DRIVER_UNKNOWN;
   }
 
+#ifdef __APPLE__
+  // Vulkan on macOS goes through Metal, and is not susceptible to the same bugs
+  // as the vendor's native Vulkan drivers. We use a different driver fields to
+  // differentiate MoltenVK.
+  driver = DriverDetails::DRIVER_PORTABILITY;
+#endif
+
   DriverDetails::Init(DriverDetails::API_VULKAN, vendor, driver,
                       static_cast<double>(m_device_properties.driverVersion),
                       DriverDetails::Family::UNKNOWN);