`ReplaySubject` with `Publisher` requirement.

replay_subject_with_publisher.swift

final class ReplaySubject<Output, Failure: Error>: Subject {
	typealias Output = Output
	typealias Failure = Failure

	private let bufferSize: Int

	init(bufferSize: Int) {
		self.bufferSize = bufferSize
	}
	
	func send(subscription: Subscription) { /* … */ }
	
	func send(completion: Subscribers.Completion<Failure>) { /* … */ }

	func send(_ value: Output) { /* … */ }

	func receive<Subscriber: Combine.Subscriber>( /// (1) The compiler’s generated method stub unfortunately picks
	/// `S` for the `Subscriber` generic. And I tend to prefer the fuller name, even though it requires a
	/// `Combine.Subscriber` disambiguation. Declarative programming is hard enough as it is and throwing
	/// single-letter generics at folks only makes it tougher.
	///
	/// Back when, Rx did the same and promoted all generics to full words in the 5.x release. See the
	/// “Generic Renames Checklist” section of [this issue](https://github.com/ReactiveX/RxSwift/issues/1921#issue-430354614)
	/// for details.
	///
	/// This method is the attachment point for subscribers to this subject. We’ll need to make sure
	/// `Subscriber.Failure` and `.Input` match `Failure` and `Output`, respectively.
		subscriber: Subscriber
	) where Failure == Subscriber.Failure, Output == Subscriber.Input { /* … */ }
}