Direct3D11 related stuff

Hi,

While implementing a library to wrap vulkan around Direct3D 11, I've noticed some very painful missing things in D3D11, that are mandatory in Vulkan :

- Support for binding ranges of a constants buffer (UBO) is missing in D3D11 on some GPUs (even though the feature is supposed to be emulated, it is effectively missing).
- D3D11 does not support copy from GPU buffer to GPU texture at all, which is very painful, especially when you work with staging buffers.

Are those things worth integrating to Vulkan-Portability ?

The issue names no files, tests, or entry points. Start by evaluating whether Vulkan-Portability can address the two reported Direct3D 11 limitations: constant-buffer range binding and GPU-buffer-to-GPU-texture copies. Done is a maintainer decision on whether these capabilities belong in the project, with the required scope identified.

Written by the indexing model from the issue text.