NoAccessLevelOnExtensionDeclaration doesn't apply access modifier on members guarded by #if

[ahoppen]

Reproducer:

public extension Foo {
#if os(ios)
    static let x = 10
#endif
    static let y = 10
}

Gets formatted to

extension Foo {
  #if os(ios)
    static let x = 10
  #endif
  public static let y = 10
}

But should be

extension Foo {
  #if os(ios)
    public static let x = 10
  #endif
  public static let y = 10
}

rdar://146604297