Invalidate biometric on change (#1026)

* Initial working version for Android

* Add a fallback for when upgrading from older app version.

* Ensure biometric validity is re-checked on focus

* Only setup biometric integrity key if biometric is turned on.

* Fix styling according to comments

* Fallback for Android 5.

* Improve comment

* Add boilerplate for iOS

* Change BiometricService to public

* Untested iOS implementation.

* Convert IBiometricService to async. Fix code style for iOS.

* Base64 NSData.

* Review comments for Android BiometricService.

* Rename methods in BiometricService to append Async

* Ensure we wait for async SetupBiometricAsync.

* Update BiometricService.cs

Co-authored-by: Kyle Spearrin <kspearrin@users.noreply.github.com>

src/Android/MainApplication.cs

@@ -98,6 +98,7 @@ namespace Bit.Droid
                 broadcasterService, () => ServiceContainer.Resolve<IEventService>("eventService"));
             var platformUtilsService = new MobilePlatformUtilsService(deviceActionService, messagingService,
                 broadcasterService);
+            var biometricService = new BiometricService();
 
             ServiceContainer.Register<IBroadcasterService>("broadcasterService", broadcasterService);
             ServiceContainer.Register<IMessagingService>("messagingService", messagingService);
@@ -108,6 +109,7 @@ namespace Bit.Droid
             ServiceContainer.Register<IStorageService>("secureStorageService", secureStorageService);
             ServiceContainer.Register<IDeviceActionService>("deviceActionService", deviceActionService);
             ServiceContainer.Register<IPlatformUtilsService>("platformUtilsService", platformUtilsService);
+            ServiceContainer.Register<IBiometricService>("biometricService", biometricService);
 
             // Push
 #if FDROID