Add HLSL memory barrier intrinsics, fix dst, add lit & EvaluateAttributeSnapped

Test/hlsl.intrinsics.f1632.frag

@@ -0,0 +1,34 @@
+float PixelShaderFunction(float inF0)
+{
+    f32tof16(inF0);
+
+    return 0.0;
+}
+
+float1 PixelShaderFunction(float1 inF0)
+{
+    // TODO: ... add when float1 prototypes are generated
+    return 0.0;
+}
+
+float2 PixelShaderFunction(float2 inF0)
+{
+    f32tof16(inF0);
+
+    return float2(1,2);
+}
+
+float3 PixelShaderFunction(float3 inF0)
+{
+    f32tof16(inF0);
+
+    return float3(1,2,3);
+}
+
+float4 PixelShaderFunction(float4 inF0)
+{
+    f32tof16(inF0);
+
+    return float4(1,2,3,4);
+}
+