texture data is not written directly to device context

[bengreenier]

This tracks an optimization that we have added in the past for https://github.com/3DStreamingToolkit/3DStreamingToolkit - wherein we store the device context and write to the device directly, rather than marshalling data up into a unity texture.

https://github.com/3DStreamingToolkit/3DStreamingToolkit/blob/master/Plugins/UnityServerPlugin/StreamingUnityServerPlugin.cpp#L339