Add low difficulty spacing checks

[Naxesss]

Makes more progress towards resolving #12091.

Adds

• CheckTimeDistanceEquality
  • Ensures the distance between objects is consistent with the time between them
  • Applies to Easy and Normal difficulties
  • Leniency to allow for placing objects by hand approximately correct
  • Rolling window to allow building up/down slowly (e.g. for maps that change BPM and/or SV)
• CheckLowDiffOverlaps
  • Ensures overlaps are done when appropriate
  • Applies to Easy difficulties
• Tests for those checks

DunfnK0a2H.mp4

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The overlap check should also apply to Normals, but only when they are the lowest difficulty in the set. I don't believe there's any way to detect that currently, given that the editor only knows of the difficulty being edited. So that's skipped for now.

[peppy]

No major issues, nice work