Fixes #1778.
+ move duration calculation to not be done twice + made Slider / Spinner private again as they are not accessed externally anymore
PositionAt is clamped to [0, 1] where 0 denotes the beginning of the curve and 1 denotes the end of the curve. It has no concept of repeats.
some things work and others don't, I dunno
silly me, that was configured for vitaru!
Plus a lot more implementation.