message: Add Buffer->Texture->Buffer copy test
  This does a Buffer->Buffer copy using a Texture as an intermediate
  resource and checks if the resulting buffer data is the same
diff: @@ -56,4 +56,44 @@ TEST_P(BasicTests, ReadPixelsTest) {
  EXPECT_PIXEL_RGBA8_EQ(red, texture, 0, 0);
  }
  +TEST_P(BasicTests, Buffer2Texture2Buffer) {
  + static constexpr unsigned int kSize = 64;
  +
  + uint8_t data[4 * kSize * kSize] = {};
  + for (unsigned int i = 0; i < 4 * kSize * kSize; ++i) {
  + data[i] = i % 256;
  + }
  +
  + nxt::Buffer srcBuffer = utils::CreateFrozenBufferFromData(device, data, 4 * kSize * kSize, nxt::BufferUsageBit::TransferSrc);
  +
  + nxt::Texture texture = device.CreateTextureBuilder()
  + .SetDimension(nxt::TextureDimension::e2D)
  + .SetExtent(kSize, kSize, 1)
  + .SetFormat(nxt::TextureFormat::R8G8B8A8Unorm)
  + .SetMipLevels(1)
  + .SetAllowedUsage(nxt::TextureUsageBit::TransferDst | nxt::TextureUsageBit::TransferSrc)
  + .GetResult();
  +
  + nxt::Buffer dstBuffer = device.CreateBufferBuilder()
  + .SetAllowedUsage(nxt::BufferUsageBit::TransferDst | nxt::BufferUsageBit::TransferSrc)
  + .SetInitialUsage(nxt::BufferUsageBit::TransferDst)
  + .SetSize(4 * kSize * kSize)
  + .GetResult();
  +
  + nxt::CommandBuffer commands = device.CreateCommandBufferBuilder()
  + .TransitionTextureUsage(texture, nxt::TextureUsageBit::TransferDst)
  + .CopyBufferToTexture(srcBuffer, 0, texture, 0, 0, 0, kSize, kSize, 1, 0)
  +
  + .TransitionTextureUsage(texture, nxt::TextureUsageBit::TransferSrc)
  + .TransitionBufferUsage(dstBuffer, nxt::BufferUsageBit::TransferDst)
  + .CopyTextureToBuffer(texture, 0, 0, 0, kSize, kSize, 1, 0, dstBuffer, 0)
  +
  + .GetResult();
  +
  + queue.Submit(1, &commands);
  +
  + const uint32_t* dataView = reinterpret_cast<uint32_t*>(data);
  + EXPECT_BUFFER_U32_RANGE_EQ(dataView, dstBuffer, 0, kSize * kSize);
  +}
  +
  NXT_INSTANTIATE_TEST(BasicTests, MetalBackend, D3D12Backend)
  