This is to modernize the API:
- Add meaningful name to all textures (except DRW textures).
- Remove unused err_out argument: only used for offscreen python.
- Add mipmap count to creation functions for future changes.
- Clarify the data usage in creation functions.
This is a cleanup commit, there is no functional change.
# Conflicts:
# source/blender/gpu/GPU_texture.h
