Substitution support in custom rules

[dankinsoid]

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• [ x ] I've Updated SwiftLint to the latest version.
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Feature Request or Enhancement Proposal

I suggest supporting substitutions in custom rules to provide contextual warnings and errors.

Example of the rule with a substitution:

    corner_radius_setter:
      name: "CornerRadius setter"
      regex: 'layer\.cornerRadius = (.+)'
      message: "Use setCornerRadius($1) instead"
      severity: warning

So for this line:

layer.cornerRadius = 34

We get the message:
Use setCornerRadius(34) instead