Adopt consecutiveSpaces rule

[calda]

Summary

This PR adopts SwiftFormat's consecutiveSpaces rule, piggybacking on top of the existing limit-vertical-whitespace rule

Limit consecutive whitespace to one blank line or space (excluding indentation). Favor the following formatting guidelines over whitespace of varying heights to divide files into logical groupings.

// WRONG
struct Planet {

  let mass:          Double
  let hasAtmosphere: Bool


  func travelTo() { }

}

// RIGHT
struct Planet {

  let mass: Double
  let hasAtmosphere: Bool

  func travelTo() { }

}

Reasoning

This aligns with the style folks are currently using, based on my experience. Linting for this will prevent folks from unintentionally introducing stray whitespace.

Please react with 👍/👎 if you agree or disagree with this proposal.