Use case

I found that using WebKitWebViewController.setAllowsBackForwardNavigationGestures(true); does not work properly.
I hope to add a callback for changes in the canGoBack property to distinguish whether WebKitWebViewController.setAllowsBackForwardNavigationGestures(false); needs to be prohibited

Proposal

Added callback for canGoBack property change
I'd be happy to create a PR if I can.