This allows to match and transfer data between two meshes with similar shape but complete arbitrary different transform.
Note that the result will be best if the meshes (more precisely, their vertices) are exact copies of each other.
Otherwise, method used can only perform an approximated best match, which means you'll likely get better
results if you 'visually' make them match in 3D space (and use 'Object Transform') instead.
Simply check and early return in case we have no source or destination items
(verts/edges/loops/polys) available...
Also, fix an assert in `BKE_mesh_calc_normals_poly()`, when called with no poly.
Titles says everything, just two notes:
* We have to actually transfer plain *normals*, not 'compressed' clnors,
so had to add pre/post process to transfer to make the conversions.
* Also added interpolation and advanced copy/mixing to CD_NORMAL, for same reasons.
Issue was, when requesting (building) lnors for a mesh that has
autosmooth disabled, one would expect to simply get vnors as lnors.
Until now, it wasn't the case, which was bad e.g. for normal projections
of loops in recent remap code (projecting along split loop normals
when you would expect projection along vertex normals...).
Also, removed the 'angle' parameter from RNA's `mesh.calc_normals_split`.
This should *always* use mesh settings (both autosmooth and smoothresh),
otherwise once again we'd get inconsistencies in some cases.
Will update fbx and obj addons too.
Mesh stores its dvert in a specific pointer too, in addition of regular CD layer...
That whole vgroup handling is really breaking apart the 'universality' of CD system. :(
Also added some DAG and WM updates in operators...
