[TIMOB-26174] Android: add setCancelable method on Ti.UI.AlertDialog

When I use the following code, I want to prevent the Android back button from dismissing the dialog, since I want to detect if a user clicked or canceled the dialog. When the dialog is canceled/dismissed via the Android back button, no event is triggered. By implementing the setCancelable method, this could be solved. See https://developer.android.com/reference/android/app/AlertDialog.Builder#setCancelable(boolean)

    var dialog = Ti.UI.createAlertDialog({
        message: pMessage,
        ok: 'OK',
        title: 'Title',
        canceledOnTouchOutside: false,
        persistent: true
    });