- Move functions that handle animation to own file - `animation.c`
- Refactor `SEQ_offset_animdata` and `SEQ_free_animdata` functions
- Add function `SEQ_fcurves_by_strip_get` to provide more granular
and explicit way for operators to handle animation
- Remove function `SEQ_dupe_animdata`, do curve duplication explicitly
in operator code, which makes more sense to do. Further this function
was also used for renaming strips which makes no sense.
- Refactor usage of function `SEQ_free_animdata` and remove XXX comment.
Now this functiuon is no longer called when `Sequence` data is freed
implicitly, it is done explicitly in high level function
`SEQ_edit_remove_flagged_sequences`
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D13852
