This patch refactors the "Hair" data-block, which will soon be renamed to "Curves". The larger change is switching from an array of `HairCurve` to find indices in the points array to simply storing an array of offsets. Using a single integer instead of two halves the amount of memory for that particular array. Besides that, there are some other changes in this patch: - Split the data-structure to a separate `CurveGeometry` DNA struct so it is usable for grease pencil too. - Update naming to be more aligned with newer code and the style guide. - Add direct access to some arrays in RNA -- Radius is now retrieved as a regular attribute in Cycles. -- `HairPoint` has been renamed to `CurvePoint` -- `HairCurve` has been renamed to `CurveSlice` - Add comments to the struct in DNA. The next steps are renaming `Hair` -> `Curves`, and adding support for other curve types: Bezier, Poly, and NURBS. Ref T95355 Differential Revision: https://developer.blender.org/D13987