Move load battery consumer icon and label into the background

move high latency icon and label loading into the background thread to
improve the performance and first frame response time, which is also the
pre-work for checking whether a item is tappable or not feature (will
work this on the next patch)

Bug: 188751551
Test: make SettingsgRoboTests
Change-Id: I4e5712e995fce055d2735135c28be60fb70e5796

src/com/android/settings/fuelgauge/BatteryDiffEntry.java

@@ -142,7 +142,7 @@ public class BatteryDiffEntry {
         return false;
     }
 
-    private void loadLabelAndIcon() {
+    void loadLabelAndIcon() {
         if (mIsLoaded) {
             return;
         }