This PR allows users to select a GPU backend.
In the system tab of the user preferences the GPU backend can be selected in the `Display Graphics` panel.
It will require a restart of Blender before the changes become effective.
During startup minimum requirements are checked. Blender will switch automatically
to OpenGL when no compatible Vulkan device could be detected. A dialog will be shown
to inform the user.
The setting of the in the `Display Graphics` panel are still overridden when blender is started
using the `--gpu-backend` option. When starting blender with `--debug-gpu` the backend
detection will print to the console.
See PR for detailed information and screenshots of the UI.
Implements #126504
Pull Request: https://projects.blender.org/blender/blender/pulls/126545
458faa6486