Rule Request: Opt-in rule that top-level constants be prefixed by k

[jpsim]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Rule Request

1. Why should this rule be added? Share links to existing discussion about what
the community thinks about this.

Some codebases (i.e. Lyft) consistently require that top-level constants be named kVarName.

2. Provide several examples of what would and wouldn't trigger violations.

// Wouldn't trigger
private let kMarginSize = 20.0
public let kFeatureEnabled = false

struct MyStruct {
    let marginSize = 20.0
}

// Would trigger
private let marginSize = 20.0
public let featureEnabled = false

3. Should the rule be configurable, if so what parameters should be configurable?

We might want to make the prefix configurable (e.g. k vs a custom value). I think it'd be fine to do this without allowing configurability for the first version and only add it if people express an interest in it.

4. Should the rule be opt-in or enabled by default? Why?
See README.md for guidelines on when to mark a
rule as opt-in.

Should definitely be opt-in as this is a non-standard stylistic choice.

[marcelofabri]

Implemented in #1991.