Change PreferenceController#getSummary return type.

Return CharSequence instead of String.

All user visible string should be modeled as CharSequence.

Bug: 73950519
Test: robotest
Change-Id: I30befef0c33f94351d4a2774e283bd1ed804aa8b

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

@@ -103,7 +103,7 @@ public class BatterySaverController extends TogglePreferenceController
     }
 
     @Override
-    public String getSummary() {
+    public CharSequence getSummary() {
         final boolean mode = mPowerManager.isPowerSaveMode();
         final int format = mode ? R.string.battery_saver_on_summary
                 : R.string.battery_saver_off_summary;