Multiple changes to get a triangle working with hacky usage of descriptor heaps

samples/descriptor_heap/shaders/heap_triangle.frag

@@ -1,9 +1,10 @@
 #version 450
-
 #pragma shader_stage(fragment)
 
+#extension GL_EXT_descriptor_heap: require
+
 layout(location = 0) out vec4 outColor;
 
 void main() {
     outColor = vec4(0.f, 1.f, 0.f, 1.f);
-}
+}