Add support for popover menus (for copy, paste etc)

[KaneCheshire]

struct PopoverMenu: Element {
	
	let id: String? = nil // There is only one menu shared across the app, and it has no ID.
	let index: Int = 0
	let type: XCUIElement.ElementType = .menu
	let parent: Element
	
	var numberOfItems: Int { return underlyingXCUIElement.descendants(matching: .menuItem).count }
	
	init(parent: Element = App.shared) {
		self.parent = parent
	}
	
	var copy: Item { return item(withID: "Copy") }
	
	func item(withID id: String) -> Item {
		return Item(id: id, parent: self)
	}
	
}

extension PopoverMenu {
	
	struct Item: Element, Tappable {
		
		let id: String?
		let type: XCUIElement.ElementType = .menuItem
		let parent: Element
		
		init(id: String, parent: PopoverMenu) {
			self.id = id
			self.parent = parent
		}
		
	}
	
}

[KaneCheshire]

These are actually called EditMenus in the HIGs: https://developer.apple.com/design/human-interface-guidelines/ios/controls/edit-menus/

[KaneCheshire]

Disregard that mention ^ as far as I can see that wasn't added so I'm not sure why I mentioned it here. Perhaps I meant to reference a different issue.