Hi all,  Currently DispatchQueue.main returns a DispatchQueue object.  I thought that returning a OS_dispatch_queue_main instead could allow clients to extend the class and add features specific to the main dispatch queue of their iOS apps for example.  One possible use case:  public extension OS_dispatch_queue_main {     func asyncIfNeeded(         group: DispatchGroup? = nil,         qos: DispatchQoS = .unspecified,         flags: DispatchWorkItemFlags = [],         execute work: @escaping () ...