Fixes#108730
The call to `CustomData_interp` also interpolated the face corner
topology attributes, which broke the mesh completely. To fix this,
avoid relying on the CustomData API and move the attribute
interpolation to use the attribute API instead. This change also
makes it trivial to support all attribute types in the future.
Also, only retrieve the closest vertex once, instead of doing it
again for every attribute. Combined with building the topology
maps in parallel this approximately doubled the performance
of color attribute propagation in a test with 2 million vertices
and 8 color attributes on both domains (63 to 34 ms).
Pull Request: https://projects.blender.org/blender/blender/pulls/108773
2b45f2d662