Custom `Publisher.share` scaffolding.

cher_ scaffolding.swift

import Combine

extension Publisher {
	func cher() -> AnyPublisher<Output, Failure> { /// (1) `cher` to avoid
		/// colliding with `share` and for now, returning `AnyPublisher`
		/// until we have a fuller type in hand. My
		/// [post on operator fusion](https://jasdev.me/fusion-primer) has
		/// more detail on the erasure and full-type dance.
		fatalError("To be implemented.")
	}
}