Add missing concrete implementation of 'WebKitWebViewController.setAllowsLinkPreview' (#1452)

Author: daohoangson

packages/fwfh_webview/test/mock_webview_platform.dart

@@ -225,6 +225,9 @@ class __FakeWebKitWebViewController extends FakeWebViewController
   Future<void> setAllowsBackForwardNavigationGestures(bool enabled) =>
       throw UnimplementedError();
 
+  @override
+  Future<void> setAllowsLinkPreview(bool allow) => throw UnimplementedError();
+
   @override
   Future<void> setOnCanGoBackChange(
     void Function(bool) onCanGoBackChangeCallback,