Move the `bAnimListElem` struct down in its header file, so that it sits underneath the `enum` types that it uses. This move is necessary for an upcoming refactor where the struct actually declares its fields to be of those enum types. Separating the move from the actual change in type will help with clarity in the diffs. No functional changes. Pull Request: https://projects.blender.org/blender/blender/pulls/122874