Move the code dealing with converting float3 to GPU normals
out of the vertex format header into a separate header. Use a
proper C++ namespace and remove duplication by only using
the more recently added C++ templated conversions.
Most of the diff comes from the removal of the indirect includes
from GPU_vertex_format.hh. A lot of files ended up mistakenly
depending on that.
Pull Request: https://projects.blender.org/blender/blender/pulls/134873
