Allows users to override the auto detection for GPU
selection. Normally the GPU selection is done by looping
over the order Vulkan provides and finding the highest
performing device based on its type (discrete, integrated,
software).
However users might have multiple discrete cards and want
to switch between them. Or developers want to validate other
GPUs without rebooting.
This PR adds the ability to override the auto detection
for the vulkan backend.
**Future improvements**:
- This PR does not include a command line option. This can be added
later for render farms.
Pull Request: https://projects.blender.org/blender/blender/pulls/127860
