Add clamp on extra descriptors in D3D12 for CBV/SRV/UAV heap. Refs #518

* We need extra descriptors during some analysis events for patching e.g
  shaders for overlays and things. This is because D3D12 only allows one
  heap of any given time bound at once.
* D3D12 also limits the size of that heap, and the limit is not
  queryable so the application can make a heap of maximum size that it
  uses all of.
* There's no solution for this, in this case we just can't add more
  descriptors and when we try to use the last one for our own purposes
  we stand a small chance of stomping an important descriptor.

renderdoc/driver/d3d12/d3d12_device.cpp

@@ -179,6 +179,10 @@ WrappedID3D12Device::WrappedID3D12Device(ID3D12Device *realDevice, D3D12InitPara
     m_DescriptorIncrements[i] =
         realDevice->GetDescriptorHandleIncrementSize(D3D12_DESCRIPTOR_HEAP_TYPE(i));
 
+  RDCEraseEl(m_D3D12Opts);
+
+  realDevice->CheckFeatureSupport(D3D12_FEATURE_D3D12_OPTIONS, &m_D3D12Opts, sizeof(m_D3D12Opts));
+
   WrappedID3D12Resource::m_List = NULL;
 
   // refcounters implicitly construct with one reference, but we don't start with any soft

renderdoc/driver/d3d12/d3d12_device.h

@@ -333,6 +333,7 @@ private:
 
   WrappedIDXGISwapChain4 *m_LastSwap;
 
+  D3D12_FEATURE_DATA_D3D12_OPTIONS m_D3D12Opts;
   UINT m_DescriptorIncrements[D3D12_DESCRIPTOR_HEAP_TYPE_NUM_TYPES];
 
   void Serialise_CaptureScope(uint64_t offset);

renderdoc/driver/d3d12/d3d12_device_wrap.cpp

@@ -447,7 +447,15 @@ bool WrappedID3D12Device::Serialise_CreateDescriptorHeap(
     // while patching, because DX12 has a stupid limitation to not be able
     // to set multiple descriptor heaps at once of the same type
     if(Descriptor.Type == D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV)
-      Descriptor.NumDescriptors += 16;
+    {
+      if(m_D3D12Opts.ResourceBindingTier == D3D12_RESOURCE_BINDING_TIER_3 ||
+         Descriptor.NumDescriptors + 16 <= 1000000)
+        Descriptor.NumDescriptors += 16;
+      else
+        RDCERR(
+            "RenderDoc needs extra descriptors for patching during analysis,"
+            "but heap is already at binding tier limit");
+    }
 
     ID3D12DescriptorHeap *ret = NULL;
     HRESULT hr = m_pDevice->CreateDescriptorHeap(&Descriptor, guid, (void **)&ret);