[5.5][Refactoring] Support refactoring calls to async if a variable or function is used as completion handler

[ahoppen]

Cherry-pick of #37314 into release/5.5

• Explanation: Async refactoring previously failed if we were using a variable as a completion handler. For example, we couldn’t refactor wrapperAroundSimple to async.

func simple(completion: (String) -> Void) {}
func simple() async -> String {}

func wrapperAroundSimple(completionHandler: (String) -> Void) {
  simple(completion: completionHandler)
}

Now we generate

func wrapperAroundSimple() async {
  return await simple()
}

Similarly, we previously failed if a function was used as completion handler

func printResultOfSimple() {
  simple(completion: print)
}

We now generate

func printResultOfSimple() async {
  let result = await simple()
  print(result)
}

• Scope: Async refactoring (add async alternative, convert to async, convert call to async)
• Risk: Low (this only affects async refactoring)
• Testing: Added new test cases to the refactoring test suite
• Issue: rdar://77460524
• Reviewer: Ben Barham (@bnbarham)

[ahoppen]

@swift-ci Please test

[ahoppen]

@swift-ci Please nominate