[d3d9] Rotate swap chain back buffers

Restores functionality removed in 81c3daa3d0.

src/d3d9/d3d9_subresource.h

@@ -111,6 +111,14 @@ namespace dxvk {
       return m_container;
     }
 
+    void Swap(D3D9Subresource* Other) {
+      // Only used for swap chain back buffers that don't
+      // have a container and all have identical properties
+      std::swap(m_texture,          Other->m_texture);
+      std::swap(m_sampleView,       Other->m_sampleView);
+      std::swap(m_renderTargetView, Other->m_renderTargetView);
+    }
+
   protected:
 
     IDirect3DBaseTexture9*  m_container;

src/d3d9/d3d9_swapchain.cpp

@@ -739,6 +739,13 @@ namespace dxvk {
 
       SubmitPresent(sync, i);
     }
+
+    // Rotate swap chain buffers so that the back
+    // buffer at index 0 becomes the front buffer.
+    for (uint32_t i = 1; i < m_backBuffers.size(); i++)
+      m_backBuffers[i]->Swap(m_backBuffers[i - 1].ptr());
+
+    m_parent->m_flags.set(D3D9DeviceFlag::DirtyFramebuffer);
   }