Sync to GPU when fence is signalled on a queue

* Dynamic descriptor writes that happen after a fence sync must be synchronised
  against the work on queues. Since we don't capture CPU-waits on fences we need
  to sync on the signal.

renderdoc/driver/d3d12/d3d12_command_queue_wrap.cpp

@@ -699,6 +699,7 @@ bool WrappedID3D12CommandQueue::Serialise_Signal(SerialiserType &ser, ID3D12Fenc
   if(IsReplayingAndReading() && pFence)
   {
     m_pReal->Signal(Unwrap(pFence), Value);
+    m_pDevice->GPUSync();
   }
 
   return true;