message: Update BufferD3D12 to use Align helper
diff: #include "backend/d3d12/ResourceAllocator.h"
  #include "backend/d3d12/ResourceUploader.h"
  #include "common/Assert.h"
  +#include "common/Constants.h"
  +#include "common/Math.h"
  namespace backend {
  namespace d3d12 {
  @@ -94,7 +96,7 @@ namespace d3d12 {
  uint32_t Buffer::GetD3D12Size() const {
  // TODO(enga@google.com): TODO investigate if this needs to be a constraint at the API level
  - return ((GetSize() + 256 - 1) / 256) * 256; // size is required to be 256-byte aligned.
  + return Align(GetSize(), 256);
  }
  ComPtr<ID3D12Resource> Buffer::GetD3D12Resource() {
  @@ -178,7 +180,7 @@ namespace d3d12 {
  uint32_t BufferView::GetD3D12Size() const {
  // TODO(enga@google.com): TODO investigate if this needs to be a constraint at the API level
  - return ((GetSize() + 256 - 1) / 256) * 256; // size is required to be 256-byte aligned.
  + return Align(GetSize(), 256);
  }
  const D3D12_CONSTANT_BUFFER_VIEW_DESC& BufferView::GetCBVDescriptor() const {
  