Add slang shaders for additional samples

shaders/slang/negativeviewportheight/quad.slang

@@ -0,0 +1,30 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+	float3 Pos;
+    float2 UV;
+};
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+    float2 UV;
+};
+
+Sampler2D samplerColor;
+
+[shader("vertex")]
+VSOutput vertexMain(VSInput input)
+{
+    VSOutput output;
+    output.UV = input.UV;
+    output.Pos = float4(input.Pos, 1.0f);
+    return output;
+}
+
+[shader("fragment")]
+float4 fragmentMain(VSOutput input)
+{
+    return samplerColor.Sample(input.UV);
+}