[Feature Request] Implement "ApproachType"

[MrThatKid]

Is your feature request related to a problem? Please describe.

When making modifiers have approach speeds that react to the song's timing, there isn't really an easy way to do this.

Describe the solution you'd like

ApproachType is a modifier in nITG that makes the modifier's approach speed be based on the current song's BPM instead of time. It might be good to port this modifier over.

Describe alternatives you've considered

Currently, it's possible to "emulate" this modifier by dividing the approach rate by the length of a beat in seconds, but this requires a lot more work depending on what the song does.