Take as Unrestricted Mode in the UI if current Mode is Unknown.

- Battery usage mode MODE_UNKNOWN is (1) apps in allowlist and (2) app's OP_RUN_ANY_IN_BACKGROUND = MODE_IGNORED.
For this case, mode should be displayed as Unrestricted on UI since it is in allowlist; and should be logged as unknown mode for the potential compatibility issues.

- After Backup & Restore, the MODE_UNKNOWN will be reset to Optimized(Default) Mode on target device.

Bug: 372831500
Test: manual
Test: atest BatteryOptimizeUtilsTest
Test: atest AppOptModeSharedPreferencesUtilsTest
Flag: EXEMPT for simple fix
Change-Id: Ic18e026f71a4a50ffa1711e2ca0782aeb8b33076

tests/robotests/src/com/android/settings/fuelgauge/BatteryOptimizeUtilsTest.java

@@ -127,6 +127,15 @@ public class BatteryOptimizeUtilsTest {
         assertThat(mBatteryOptimizeUtils.getAppOptimizationMode()).isEqualTo(MODE_OPTIMIZED);
     }
 
+    @Test
+    public void testGetAppOptimizationMode_unknownMode_returnOptimized() throws Exception {
+        when(mMockBackend.isAllowlisted(anyString(), anyInt())).thenReturn(true);
+        when(mMockAppOpsManager.checkOpNoThrow(anyInt(), anyInt(), anyString()))
+                .thenReturn(AppOpsManager.MODE_IGNORED);
+
+        assertThat(mBatteryOptimizeUtils.getAppOptimizationMode()).isEqualTo(MODE_UNRESTRICTED);
+    }
+
     @Test
     public void testIsSystemOrDefaultApp_isSystemOrDefaultApp_returnTrue() {
         when(mMockBackend.isAllowlisted(anyString(), anyInt())).thenReturn(true);