WKWebView and UIMenuController

For iOS 11, simply subclass WKWebView and override canPerformAction to return false:

class WebView : WKWebView {
    override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
        return false
    }
}

For iOS 10 or earlier, swizzle WKContentView's canPerformAction method:

@objc private extension UIResponder {
    func swizzle_canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
        return false
    }
}

guard let viewClass = NSClassFromString("WKContentView") as? UIView.Type else { return }
method_exchangeImplementations(
    class_getInstanceMethod(viewClass, #selector(UIResponder.canPerformAction))!,
    class_getInstanceMethod(UIResponder.self, #selector(UIResponder.swizzle_canPerformAction))!
)

After remove those web view's build-in menu items, you can add your custom menu items via UIMenuController.shared like normal.

This appears to be fixed in iOS 13 beta 1.