PM-3349 Implemented HybridWebViewHandler for Android which enables 2nd factor auth flows

Ensured CustomTabbedPageHandler had it's DisconnectHandler called
Some minor code upgrades of older obsolete Xamarin Forms code.

src/Core/Controls/HybridWebView.cs

@@ -1,8 +1,4 @@
-using System;
-using Microsoft.Maui.Controls;
-using Microsoft.Maui;
-
-namespace Bit.App.Controls
+namespace Bit.App.Controls
 {
     public class HybridWebView : View
     {