Merge pull request #460 from wxmarr/feature/flutter_1.9_upgrade

暴露createFlutterView，供在flutterView add 原生view

android/src/main/java/com/idlefish/flutterboost/containers/NewBoostFlutterActivity.java

@@ -228,7 +228,7 @@ public class NewBoostFlutterActivity extends Activity
     }
 
     @NonNull
-    private View createFlutterView() {
+    protected View createFlutterView() {
         return delegate.onCreateView(
                 null /* inflater */,
                 null /* container */,