Update UI for factory reset flow

After applying a collapsing toolbar in the Settings app, the factory
reset screen is not displayed correctly. This is because
1) the factory reset page should not essentially have a toolbar since it
has different UI layout form other pages.
2) this page was launched previously as a SubSettings so it applied a
wrong theme.

This change is mainly updating the inheritence structure and specifying
the right theme for the factory reset page in order to have a correct
layout.

Bug: 179457252
Test: robotests and visual verified
Change-Id: I91aec65a120d5a288507d89ace7c9298acdca42b

src/com/android/settings/system/FactoryResetPreferenceController.java

@@ -16,9 +16,13 @@
 package com.android.settings.system;
 
 import android.content.Context;
+import android.content.Intent;
 import android.os.UserManager;
 
+import androidx.preference.Preference;
+
 import com.android.settings.R;
+import com.android.settings.Settings;
 import com.android.settings.Utils;
 import com.android.settings.core.PreferenceControllerMixin;
 import com.android.settingslib.core.AbstractPreferenceController;
@@ -45,4 +49,14 @@ public class FactoryResetPreferenceController extends AbstractPreferenceControll
     public String getPreferenceKey() {
         return KEY_FACTORY_RESET;
     }
+
+    @Override
+    public boolean handlePreferenceTreeClick(Preference preference) {
+        if (KEY_FACTORY_RESET.equals(preference.getKey())) {
+            final Intent intent = new Intent(mContext, Settings.FactoryResetActivity.class);
+            mContext.startActivity(intent);
+            return true;
+        }
+        return false;
+    }
 }