This PR performs the following refactors in sculpt_trim.cc:
* Remove `depth_front` and `depth_back` as `struct` properties, as they
are only used for generating the Mesh
* Moves the `calculate_depth` call into the `generate_geometry` step as
the latter is dependent on data from the former already
* Reorganize the methods so the overall file reads better.
* Minor comment nits and additions
Pull Request: https://projects.blender.org/blender/blender/pulls/120331
2582664f67