reject metal surface creation when extension not enabled

[aizu-m]

loader_wsi_tests.cpp: Failure
Expected equality of these values:
  VK_ERROR_EXTENSION_NOT_PRESENT
  vkCreateMetalSurfaceEXT(inst, &surf_create_info, nullptr, &surface)
    Which is: VK_SUCCESS

Went through each surface terminator's disabled-extension branch. terminator_CreateMetalSurfaceEXT logs the "extension not enabled" warning and then keeps going: it allocates the VkIcdSurface, copies the create_info and returns the handle with VK_SUCCESS. The other Create*Surface terminators refuse that branch, most returning VK_ERROR_EXTENSION_NOT_PRESENT. Metal is the only one that hands back a live surface for an extension the caller never enabled.

The vkGetInstanceProcAddr gate hides this on the usual resolution path, but the exported vkCreateMetalSurfaceEXT trampoline reaches the terminator directly, as does a layer calling down the chain. Fix sets the error and jumps to the shared cleanup so the behaviour matches the siblings. Added a regression test that drives the exported entrypoint on an instance that only enabled VK_KHR_surface.

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