Update colon spacing rule to apply to dictionary literals

[calda]

Summary

This PR proposes updating the existing colon-spacing rule to also apply to dictionary literals. Previously, it applied to all usage of commas except dictionary literals.

// WRONG
let moons: [Planet : Moon] = [
  mercury : [], 
  venus : [], 
  earth : [theMoon], 
  mars : [phobos,deimos],
]

// RIGHT
let moons: [Planet: Moon] = [
  mercury: [], 
  venus: [], 
  earth: [theMoon], 
  mars: [phobos,deimos],
]

Reasoning

It is much more common to omit the space before colon in dictionary literals. This also makes the rule more consistent and general.

This will also let us replace the SwiftLint colon rule with the SwiftFormat spaceAroundOperators rule. The SwiftLint rule has a apply_to_dictionaries: false option to exclude dictionary literals, but the SwiftFormat rule currently does not.

[calda]

Improved the existing examples to follow the theme used elsewhere in the style guide

[calda]

Strong support for this change internally 👍🏻