No functional changes.
Clean up the code by:
* renaming variable `ks` to `keyingset`
* renaming variable `ksi` to `keyingset_info`
* renaming variable `ksp` to `keyingset_path`
* moving variables closer to where they are used
* making variables const if possible
* use `LISTBASE_FOREACH_MUTABLE` where applicable
* Fix comment style
* Remove comments that provide no extra information
Pull Request: https://projects.blender.org/blender/blender/pulls/117062
f24b7749b5