[webview_flutter] Add support to return null in PlatformWebViewController.setOnJavaScriptTextInputDialog #145799
Description
The method WebViewController.setOnJavaScriptTextInputDialog should be able to return null. It currently requires a nonnull String.
Based on the documentation for Javascript prompt and WebChromClient.onJsPrompt, this method should support returning a null value for the scenario that a user cancels the operation to enter text.
This would require a change to the platform interface, so it would need to follow https://github.com/flutter/flutter/wiki/Contributing-to-Plugins-and-Packages#changing-federated-plugins