HLSL: Plumb in HLSL parse context and keywords, and most basic HLSL parser and test.

Test/hlsl.frag

@@ -0,0 +1,11 @@
+//float4x4 World;
+//float4x4 View;
+//float4x4 Projection;
+//
+//float4 AmbientColor = float4(1, 1, 1, 1);
+//float AmbientIntensity = 0.1;
+//
+//float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
+//{
+//    return AmbientColor * AmbientIntensity;
+//}