- Remove "take ownership" argument which was confusing and always true
- The argument made ownership very confusing
- Better to avoid boolean arguments that switch a function's purpose
- Remove "mask" argument which was basically wrong and not used properly
- "EVERYTHING" was used because developers are wary of removing data
- Instead use `CD_MASK_MESH` for its purpose of original mesh data
- Remove use of shallow copied temporary mesh, which is unnecessary now
- Split shape key processing into separate functions and use C++ types
- Copy fields explicitly rather than using memcpy for the whole struct
- Use higher level functions and avoid redundant code
- The whole idea is pretty simple and can be built from standard logic
- Adjust `CustomData` logic to be consistent with "assign" expectations
- Clear the layer data from the source, and moves the anonymous ID
Differential Revision: https://developer.blender.org/D15857
21f2bacad9