dxgi: swapchains for Direct3D 12 devices that present through Vulkan; d3d9: 64-bit frontend kill switch

Two commits from the 125hz fork, rebased on ios-port:

• dxgi: a Direct3D 12 device on Vulkan (vkd3d-proton) gets an IDXGISwapChain4 that wraps vkd3d-proton's swapchain (IDXGIVkSwapChainFactory, surfaces through vkCreateWin32SurfaceKHR); windowed only. MADEIRA_DXGI_VK_SWAPCHAIN=0 restores the old "Unsupported device type" refusal. For the Vulkan routes PR on willfaust/Madeira.
• d3d9: a kill switch for the 64-bit DXMT frontend (for willfaust/Madeira #242).

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