Add feature flag for battery settings page.

Create PowerUsageSummaryLegacy and power_usage_summary_legacy, which
contains the old implementaion.

Bug: 69797586
Test: RunSettingsRoboTests
Change-Id: Icb9c25f06889462a6eedea48ae166043a6636848

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

@@ -115,4 +115,9 @@ public interface PowerUsageFeatureProvider {
      * enabled. This string notifies users that the estimate is using enhanced prediction.
      */
     String getAdvancedUsageScreenInfoString();
+
+    /**
+     * Checks whether to display the battery v2.
+     */
+    boolean isBatteryV2Enabled();
 }