Refactor FeatureFactory

Not use reflection, sets the FeatureFactoryImpl in SettingsApplication
instead.

Bug: 286764889
Test: m Settings
Test: m SettingsSpaUnitTests
Test: m RunSettingsRoboTests
Change-Id: I881bf1009a94222fc89578d14a6792a6e1507be2

tests/unit/src/com/android/settings/testutils/FakeFeatureFactory.java

@@ -95,8 +95,9 @@ public class FakeFeatureFactory extends FeatureFactory {
      * Call this in {@code @Before} method of the test class to use fake factory.
      */
     public static FakeFeatureFactory setupForTest() {
-        sFactory = new FakeFeatureFactory();
-        return (FakeFeatureFactory) sFactory;
+        FakeFeatureFactory factory = new FakeFeatureFactory();
+        setFactory(getAppContext(), factory);
+        return factory;
     }
 
   /**