Update Network & internet->Wi-Fi to use MasterSwitchPreference.

- Add a preference controller for Network & internet->Wi-Fi to control
  the preference toggling and summary update.
- Refactor WifiSettings and WifiEnabler to share code between the new
  wifi preference controller and the wifi setting.
- Refactor BluetoothSummaryHelper to have a common base class with the
  WifiSummaryHelper.
- Rename the summary helper to summary updater.

Bug: 34280769
Test: make RunSettingsRoboTests
Change-Id: I00ebfc161bcef89331bb41ba405ed8cb8232d248

tests/robotests/src/com/android/settings/bluetooth/BluetoothSettingsSummaryProviderTest.java

@@ -63,7 +63,7 @@ public class BluetoothSettingsSummaryProviderTest {
         mSummaryProvider.setListening(true);
 
         verify(mBluetoothManager.getEventManager()).registerCallback(
-            mSummaryProvider.mSummaryHelper);
+            mSummaryProvider.mSummaryUpdater);
     }
 
     @Test
@@ -71,7 +71,7 @@ public class BluetoothSettingsSummaryProviderTest {
         mSummaryProvider.setListening(false);
 
         verify(mBluetoothManager.getEventManager()).unregisterCallback(
-            mSummaryProvider.mSummaryHelper);
+            mSummaryProvider.mSummaryUpdater);
     }
 
     @Test