WIP: D3D11VA support

Overlays work, but drawing the actual video is unimplemented

app/shaders/d3d11_overlay_pixel.hlsl

@@ -0,0 +1,13 @@
+Texture2D theTexture : register(t0);
+SamplerState theSampler : register(s0);
+
+struct ShaderInput
+{
+    float4 pos : SV_POSITION;
+    float2 tex : TEXCOORD0;
+};
+
+float4 main(ShaderInput input) : SV_TARGET
+{
+    return theTexture.Sample(theSampler, input.tex);
+}