Make iOS work again with our Vulkan (Metal) backend

[JCash]

It builds, but when running it, it fails on:

On-screen rendering requires a layer of type CAMetalLayer.
ERROR:GRAPHICS: Could not create window surface for Vulkan, reason: VK_ERROR_INITIALIZATION_FAILED.
FATAL:ENGINE: Could not open window (-2).

It seems we don't do the correct implementation of the layerClassfunction, so that the device instead chooses the default EAGL layer.

[JCash]

Also, it seems we don't set the glfwSetViewType(GLFW_NO_API); inside graphics_vulkan.cpp, due to the integration of the Switch branch.

It is correct that graphics_vulkan.cpp shouldn't have any dependency on dmglfw, since that doesn't hold the windowing functions for all platforms (i.e. switch).