Add slang shaders for headless samples

shaders/slang/renderheadless/triangle.slang

@@ -0,0 +1,32 @@
+/* Copyright (c) 2025, Sascha Willems
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ */
+
+struct VSInput
+{
+    float3 Pos;
+    float3 Color;
+};
+
+struct VSOutput
+{
+    float4 Pos : SV_POSITION;
+    float3 Color;
+};
+
+[shader("vertex")]
+VSOutput vertexMain(VSInput input, uniform float4x4 mvp)
+{
+	VSOutput output;
+	output.Color = input.Color;
+	output.Pos = mul(mvp, float4(input.Pos.xyz, 1.0));
+	return output;
+}
+
+[shader("fragment")]
+float4 fragmentMain(VSOutput input)
+{
+	return float4(input.Color, 1.0);
+}