Create DataUsageListAppsController

Move apps group logic from DataUsageList.

Also add key to AppDataUsagePreference, which reduce flaky and keep
scroll position when back from app detail page.

Bug: 290856342
Test: manual - on DataUsageList
Test: unit test
Change-Id: I61e2b6bd9b192b7230e3553dbc6038f5d59bd303

src/com/android/settings/datausage/AppDataUsagePreference.java

@@ -38,6 +38,7 @@ public class AppDataUsagePreference extends AppPreference {
     public AppDataUsagePreference(Context context, AppItem item, int percent,
             UidDetailProvider provider) {
         super(context);
+        setKey("app_data_usage_" + item.key);
         mItem = item;
         mPercent = percent;