Previously, gl->DXOpenDeviceNV was called twice using dxva2 with dxinterop. AMD
drivers refused to allow this. With this commit, context_dxinterop sets its own
implementation of MPGetNativeDisplay, which can return either a
IDirect3DDevice9Ex or a dxinterop_device_HANDLE depending on the "name" request
string. hwdec_dxva2gldx then requests both of these avoiding the need to call
gl->DXOpenDeviceNV a second time.
The WGL_NV_DX_interop spec says that a shared IDirect3DSurface9 must not
be lockable, but off-screen plain surfaces are always lockable and using
them causes Nvidia drivers to crash. Use a rendertarget for the shared
surface instead.
This also changes the name of the DX_interop handle for the rendertarget
to match the name of the DirectX object (rather than the GL one) to
match the convention used in context_dxinterop.c.
