Replace per-element xform functions with numpy vectorized functions.
Setting a stride larger than item_size remains supported despite being unused.
Setting a stride smaller than item_size is not implemented.
The only specific change to a geometry layer is that vertex and polygon normals are now expanded to loop normals using numpy and foreach_set.
The overall speedup will vary depending on what layers are being imported, how many and which mapping is being used for each layer.
This can result in a large speedup for imports that have many layers, especially larger layers such as UVs and vertex colors.
Since this patch uses foreach_set it does mean that the new functions are limited to importing into blender data that is exposed to the Python API as bpy_prop_collection instances.
All existing imported geometry layers meet this criterion.
