Add standalone testbed

imgui/StandaloneImGuiTestbed/Shaders/SPIR-V/imgui-frag.glsl

@@ -0,0 +1,16 @@
+#version 450
+
+#extension GL_ARB_separate_shader_objects : enable
+#extension GL_ARB_shading_language_420pack : enable
+
+layout(set = 1, binding = 0) uniform texture2D FontTexture;
+layout(set = 0, binding = 1) uniform sampler FontSampler;
+
+layout (location = 0) in vec4 color;
+layout (location = 1) in vec2 texCoord;
+layout (location = 0) out vec4 outputColor;
+
+void main()
+{
+    outputColor = color * texture(sampler2D(FontTexture, FontSampler), texCoord);
+}