bug 15022: Need a way to specify dummy descriptors for unused bindings (WIP)

Add binding to VkDescriptorSetLayoutBinding.

https://cvs.khronos.org/bugzilla/show_bug.cgi?id=15022
diff --git a/layers/draw_state.h b/layers/draw_state.h
index 3aa9494..83b494b 100755
--- a/layers/draw_state.h
+++ b/layers/draw_state.h
@@ -148,6 +148,7 @@
     uint32_t                        endIndex; // last index of this layout
     vector<VkDescriptorType>        descriptorTypes; // Type per descriptor in this layout to verify correct updates
     vector<VkShaderStageFlags>      stageFlags; // stageFlags per descriptor in this layout to verify correct updates
+    unordered_set<uint32_t>         bindings;
 } LAYOUT_NODE;
 // Store layouts and pushconstants for PipelineLayout
 struct PIPELINE_LAYOUT_NODE {