Because we're moving to layered actions, which don't store their
fcurves in a list base, we need to update the places that assume the old
listbase-based structure.
This commit addresses the low-hanging fruit where code was previously
using the `LISTBASE_FOREACH` macro on a listbase of fcurves and it was
fairly obvious how to correctly update the code with minimal changes.
Other cases that either weren't immediately obvious or required
non-trivial code changes (or both) have been left for future PRs.
Additionally, uses of the list base that didn't use `LISTBASE_FOREACH`
were not investigated as part of this PR, whether trivial to update or
not.
Ref: #123424
Pull Request: https://projects.blender.org/blender/blender/pulls/127920
4bfa0de388