[Refactoring] Move async refactorings into their own files

lib/Refactoring/Async/DeclReferenceFinder.cpp

@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "AsyncRefactoring.h"
+
+using namespace swift;
+using namespace swift::refactoring::asyncrefactorings;
+
+bool DeclReferenceFinder::walkToExprPre(Expr *E) {
+  if (auto DRE = dyn_cast<DeclRefExpr>(E)) {
+    if (DRE->getDecl() == Search) {
+      HasFoundReference = true;
+      return false;
+    }
+  }
+  return true;
+}
+
+bool DeclReferenceFinder::containsReference(ASTNode Node,
+                                            const ValueDecl *Search) {
+  DeclReferenceFinder Checker(Search);
+  Checker.walk(Node);
+  return Checker.HasFoundReference;
+}