Add slang shaders for screenshot sample

shaders/slang/screenshot/mesh.slang

@@ -0,0 +1,60 @@
+/* Copyright (c) 2025, Sascha Willems
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ */
+
+ struct VSInput
+ {
+	float3 Pos;
+	float3 Normal;
+	float3 Color;
+ };
+ 
+ struct VSOutput
+ {
+	float4 Pos : SV_POSITION;
+	float3 Color;
+	float3 Normal;
+	float3 ViewVec;
+	float3 LightVec;
+ };
+
+struct UBO
+{
+	float4x4 projection;
+	float4x4 view;
+	float4x4 model;
+};
+ConstantBuffer<UBO> ubo;
+
+[shader("vertex")]
+VSOutput vertexMain(VSInput input)
+{
+    VSOutput output;
+    output.Normal = input.Normal;
+    output.Color = input.Color;
+
+    output.Pos = mul(ubo.projection, mul(ubo.view, mul(ubo.model, float4(input.Pos.xyz, 1.0))));
+
+    output.Normal = mul((float3x3)ubo.model, input.Normal);
+    float4 pos = mul(ubo.model, float4(input.Pos, 1.0));
+
+	const float3 lightPos = float3(1.0, -1.0, 1.0);
+    output.LightVec = lightPos.xyz - pos.xyz;
+    output.ViewVec = -pos.xyz;
+    return output;
+}
+
+[shader("fragment")]
+float4 fragmentMain(VSOutput input)
+{
+    const float ambient = 0.1;
+	float3 N = normalize(input.Normal);
+    float3 L = normalize(input.LightVec);
+    float3 V = normalize(input.ViewVec);
+    float3 R = reflect(-L, N);
+    float3 diffuse = max(dot(N, L), 0.0).rrr;
+    float3 specular = pow(max(dot(R, V), 0.0), 32.0);
+    return float4((ambient + diffuse) * input.Color.rgb + specular, 1.0);
+}