9a28e1d1b8
Semantically this is where those methods belong anyway, and it's needed for upcoming work on the RNA API. This also adds a method `KeyframeStrip::channelbag_for_slot_ensure()` to make some of the things that used to be done with `KeyframeStrip::fcurve_find_or_create()` less inconvenient in the face of the latter moving to `ChannelBag::fcurve_find_or_create()`. Pull Request: https://projects.blender.org/blender/blender/pulls/124973