Change the implementation of the raycast and sample nearest surface
node to split separate loops into separate multi-functions. This
clarifies the task of each function, gives more information to the
field evaluator, and gives more opportunity for memory reuse.
Sampling mesh attributes with triangle barycentric weights is now
implemented in a single place. Two other new multi-functions
handle conversion of sampled positions into barycentric weights.
Normalizing the ray directions for the raycast node is split out
too, so it can be skipped in some cases in the future.
The mesh attribute interpolator helper class is also removed,
since it didn't give much benefit over a more functional approach.
I didn't notice a performance improvement from this change.
Pull Request: https://projects.blender.org/blender/blender/pulls/107563
7ff752b789