unused_closure_parameter: fails to detect escaped identifiers.

[lhunath]

New Issue Checklist

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

Describe the bug

Swiftlint's unused closure parameter rule fails to detect uses of the identifier in contexts where it is quoted with single-ticks. This is particularly crucial for identifiers that have the same name as keywords. The result is false-positives.

Complete output when running SwiftLint, including the stack trace and command used

$ cat test.swift
let _: (String) -> String = { `break` in `break` }
$ swiftlint lint test.swift
Linting Swift files at paths test.swift
Linting 'test.swift' (1/1)
test.swift:1:31: warning: Unused Closure Parameter Violation: Unused parameter "break" in a closure should be replaced with _. (unused_closure_parameter)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.43.1
• Installation method used (Homebrew, CocoaPods, building from source, etc)? homebrew
• Which Xcode version are you using (check xcodebuild -version)? Xcode 12.5.1, Build version 12E507

[lhunath]

Didn't do a good job searching.
#3628