In preparation to remove `DistancedHitObjectComposer`, split off
`IPositionSnapProvider` from `IDistanceSnapProvider`.
`DistancedHitObjectComposer` was not touching `IPositionSnapProvider`'s
only interface member at all, it was just forwarding it for subclasses
to override to their own leisure.
This regressed with https://github.com/ppy/osu/pull/20850 because the
function was used in other places which expect it to factor slider
velocity into the equation.
Rather than reverting, I've added a new argument, as based on the method
naming alone it was hard to discern whether SV should actually be
considered.
The reason for the change in #20850 was to avoid the SV coming in from a
reference object which may not have a correct SV in the first place. In
such cases, passing `false` to the function will give the expected
behaviour.
