Add support for the iOS 18 text editing context menu "Writing Tools"

And the writing tools themselves:

protocol UITextInput {
    @available(iOS 18.0, macOS 15.0, *)
    optional var isEditable: Bool { get }
}

https://developer.apple.com/videos/play/wwdc2024/10168/?time=543

macOS issue at #150453
WebKit issue at #150965