Alternate method is to expose a `SnapDistancesChanged` event in
`IPositionSnapProvider` instead, but I chose this way as an analogue to
`IBeatSnapProvider.BeatDivisor`, which might even make sense to be
exposed as `BindableBeatDivisor` instead of caching that separately.
This results in slider placement including "excess" length, where the
curve is not applied to the placed path. This is generally not what we
want.
I considered adding a bool parameter (or enum) to change the
floor/rounding mode, but on further examination I think this is what we
always expect from this function.
