F-Curve interpolation uses the `FCURVE_INT_VALUES` and
`FCURVE_DISCRETE_VALUES` flags, which were not set in the keyframe
insertion function for slotted Actions. This is now resolved by making
the RNA property type part of the `FCurveDescriptor`.
Existing code has been refactored a bit, mostly to allow calling
`update_autoflags_fcurve_direct()` with just the RNA property type,
instead of passing the property itself. This avoided the need to include
pointers to RNA properties in `FCurveDescriptor`, which I think is a
slightly nicer design. It also makes it more explicit which aspect of
the property is used.
Because there's now another `std::optional<>` in the `FCurveDescriptor`,
I've also changed some `std::nullopt` to `{}` for brevity of the code,
as repeating that another time would have caused longer lines with more
rewrapping.
Pull Request: https://projects.blender.org/blender/blender/pulls/136446
a7d787f5b9