[swift-3.0-branch] Foundation: add a custom AnyHashable representation for NSSet

[moiseev]

• Explanation: Add a custom AnyHashable representation for NSSet
• Scope of Issue: Fixes the bridging in case where NSSet is a key in a Dictionary
• Origination:
• Risk: Minimal
• Reviewed By: Doug Gregor
• Testing: Existing test suite.
• Directions for QA: N/A

PR against master: #4810
rdar://problem/28330040

[moiseev]

@swift-ci Please test

[swift-ci]

Build failed
Jenkins build - Swift Test OS X Platform
Git Commit - 14d2046a4f0d13197758c694a1e9cf886c96b3de
Test requested by - @moiseev

[tkremenek]

This fails on macOS:

17:20:23 
/Users/buildnode/jenkins/workspace/swift-PR-osx/branch-swift-3.0-branch/swift/test/1_stdlib/NSSetAPI.swift:65:7: error: use of unresolved identifier 'expectNotNil'
17:20:23     = expectNotNil((anyHashable.base as! Set<AnyHashable>).first!) {
17:20:23       ^~~~~~~~~~~~
17:20:23 StdlibUnittest.expectNotEqual:1:13: note: did you mean 'expectNotEqual'?
17:20:23 public func expectNotEqual<T : Equatable>(_ expected: T, _ actual: T, _ message: @autoclosure () -> String = default, stackTrace: StdlibUnittest.SourceLocStack = default, showFrame: Bool = default, file: String = #file, line: UInt = #line)
17:20:23             ^
17:20:23 StdlibUnittest.expectNotEqual:1:13: note: did you mean 'expectNotEqual'?
17:20:23 public func expectNotEqual<T : Equatable>(_ expected: T?, _ actual: T?, _ message: @autoclosure () -> String = default, stackTrace: StdlibUnittest.SourceLocStack = default, showFrame: Bool = default, file: String = #file, line: UInt = #line)

[gribozavr]

@moiseev expectNotNil => expectNotEmpty would fix this.

[moiseev]

@swift-ci Please test

[tkremenek]

@swift-ci test linux

[tkremenek]

@swift-ci test macOS