Add builtin unlit surface path

engine/assets/builtin/shaders/unlit/unlit.vs.hlsl

@@ -0,0 +1,29 @@
+// XC_BUILTIN_UNLIT_D3D12_VS
+cbuffer PerObjectConstants : register(b1) {
+    float4x4 gProjectionMatrix;
+    float4x4 gViewMatrix;
+    float4x4 gModelMatrix;
+    float4x4 gNormalMatrix;
+    float4 gMainLightDirectionAndIntensity;
+    float4 gMainLightColorAndFlags;
+};
+
+struct VSInput {
+    float3 position : POSITION;
+    float3 normal : NORMAL;
+    float2 texcoord : TEXCOORD0;
+};
+
+struct PSInput {
+    float4 position : SV_POSITION;
+    float2 texcoord : TEXCOORD0;
+};
+
+PSInput MainVS(VSInput input) {
+    PSInput output;
+    float4 positionWS = mul(gModelMatrix, float4(input.position, 1.0f));
+    float4 positionVS = mul(gViewMatrix, positionWS);
+    output.position = mul(gProjectionMatrix, positionVS);
+    output.texcoord = input.texcoord;
+    return output;
+}