ANGLE D3D11 Buffer11::PackStorage stale-staging type confusion

Target: Windows Chrome with ANGLE D3D11 backend (the default).
Reaches Buffer11::PackStorage::packPixels twice with the same PIXEL_PACK_BUFFER, first against a TEXTURE_3D layer, then against a TEXTURE_2D_ARRAY layer of identical W×H and internal format. The second call reuses the cached ID3D11Texture3D staging texture and issues CopySubresourceRegion with a depth-OOB pSrcBox and a 2D→3D resource-dimension mismatch — documented D3D11 undefined behaviour.