pattern_matching_keywords should not trigger in some cases

[blindmonkey]

New Issue Checklist

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

Describe the bug

pattern_matching_keywords opt-in rule will warn this type of code.

let z = 3
switch foo {
case (let x, let y, z): break
}

When matching a pattern it may be desirable to bind some elements of the tuple while comparing others to an existing variable. Currently, pattern_matching_keywords simply counts the number of lets and vars, causing it to miss cases like this.

Environment

• SwiftLint version (run swiftlint version to be sure)? Verified via unit tests on master
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Built from source
• Paste your configuration file:

opt_in_rules:
  - pattern_matching_keywords

• Which Xcode version are you using (check xcodebuild -version)? Xcode 13.2.1, Build version 13C100