Add a DescriptorType to GetDescriptors query

* This will be optional in many cases but for some situations might be required
  when type information is not implicitly available in the descriptor store.
  Generally it should always be available unless the descriptor store is being
  viewed 'blank' purely from its contents with no other context.

qrenderdoc/Windows/PipelineState/GLPipelineStateViewer.cpp

@@ -485,6 +485,8 @@ void GLPipelineStateViewer::OnEventChanged(uint32_t eventId)
     range.offset = 0;
     range.descriptorSize = state->descriptorByteSize;
     range.count = state->descriptorCount;
+    // GL doesn't need the descriptor type, it has internal type information
+    range.type = DescriptorType::Unknown;
 
     rdcarray<DescriptorRange> ranges = {range};