In the animation transform code, `T_AUTOMERGE` was used to indicate that the duplicated keys need to be merged. In perparation of #111051, this no longer makes much sense because in grease pencil we cannot have two keys in the same channel at the same frame. This PR replaces the `T_AUTOMERGE` flag in the animation code to `T_DUPLICATED_KEYS` to indicate that the transform is being called with duplicated keyframes. Pull Request: https://projects.blender.org/blender/blender/pulls/111268