False positive for `redundant_nil_coalescing` for double Optional.

New Issue Checklist

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

Describe the bug

False positive for redundant_nil_coalescing check when we have double Optional.

Consider the following code:

import Foundation

func myFirstFunc() -> String?? {
    nil
}
func mySecondFunc() -> String? {
    return myFirstFunc() ?? nil
}

Note that this ?? nil is not redundant because of the double Optional returned by the first function. So this is a false positive for redundant_nil_coalescing.

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

$ ./swiftlint example.swift
Linting Swift files at paths example.swift
Linting 'example.swift' (1/1)
example.swift:7:26: warning: Redundant Nil Coalescing Violation: nil coalescing operator is only evaluated if the lhs is nil, coalescing operator with nil as rhs is redundant (redundant_nil_coalescing)
Done linting! Found 1 violation, 0 serious in 1 file.

Furthermore, when we run

$ ./swiftlint --fix example.swift
Correcting Swift files at paths example.swift
Correcting 'example.swift' (1/1)
example.swift:7:25 Corrected Redundant Nil Coalescing
Done correcting 1 file!

, it removes the ?? nil from the second function, resulting in

func mySecondFunc() -> String? {
    return myFirstFunc()
}

which actually makes the code fail to compile with error

error: value of optional type 'String??' must be unwrapped to a value of type 'String?'
 return myFirstFunc()
 ^

Environment

• SwiftLint version (run swiftlint version to be sure)?
  • 0.50.3
• Installation method used (Homebrew, CocoaPods, building from source, etc)?
  • portable_swiftlint from https://github.com/realm/SwiftLint/releases/download/0.50.3/portable_swiftlint.zip
• Paste your configuration file:

opt_in_rules:
  - redundant_nil_coalescing

• Are you using nested configurations?
  If so, paste their relative paths and respective contents.
  • No
• Do you have a sample that shows the issue? Run echo "[string here]" | swiftlint lint --no-cache --use-stdin --enable-all-rules
  to quickly test if your example is really demonstrating the issue. If your example is more
  complex, you can use swiftlint lint --path [file here] --no-cache --enable-all-rules.

import Foundation

func myFirstFunc() -> String?? {
    nil
}
func mySecondFunc() -> String? {
    // This triggers a violation:
    return myFirstFunc() ?? nil
}

Start by reproducing the report with the Swift code in example.swift and the redundant_nil_coalescing rule, using the reported swiftlint command. Trace the rule and its correction behavior for String??, then verify that linting no longer reports this case and that swiftlint --fix does not produce code that fails to compile.