[NFC] Move testing support files into their own directory (#23)

Author: phausler

Tests/AsyncAlgorithmsTests/Locking.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift Async Algorithms open source project
 //
-// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Copyright (c) 2022 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

Tests/AsyncAlgorithmsTests/Failure.swift renamed to Tests/AsyncAlgorithmsTests/Support/Failure.swift

@@ -0,0 +1 @@
+../../../Sources/AsyncAlgorithms/Locking.swift