Add a query to determine logical identifiers for descriptors

* This is a consideration for any cases where binding numbers are relevant -
  primarily D3D11 and GL - where the offset into an arbitrary (and possibly
  fake) descriptor storage is not helpful but knowing the register binding
  definitely is.
* If someone wants to look at the raw descriptor contents without respect to a
  particular shader access they can use this query to determine a more useful
  'name' for any given descriptor. On D3D11 and GL this gives the register
  number, on Vulkan it gives the binding number (and array element). On D3D12 it
  just repeats the offset effectively.

renderdoc/core/image_viewer.cpp

@@ -280,6 +280,11 @@ public:
     return ret;
   }
   rdcarray<DescriptorAccess> GetDescriptorAccess(uint32_t eventId) { return {}; }
+  rdcarray<DescriptorLogicalLocation> GetDescriptorLocations(ResourceId descriptorStore,
+                                                             const rdcarray<DescriptorRange> &ranges)
+  {
+    return {};
+  }
   DriverInformation GetDriverInfo()
   {
     DriverInformation ret = {};