Implement OP_SYSTEM_EXEMPT_FROM_POWER_RESTRICTIONS exemption

OP_SYSTEM_EXEMPT_FROM_POWER_RESTRICTIONS details:
* An app with this appop will be made exempt from all
  power restrictions, including app standby and doze.
* In addition, the app will be able to start fgs from
  the bg, and the user will not be able to stop fgs
  run by the app.

Changes:
* Implement the OP_SYSTEM_EXEMPT_FROM_POWER_RESTRICTIONS

Bug: 246330879
Test: atest PowerAllowlistBackendTest

Manual testing:
- Give OP_SYSTEM_EXEMPT_FROM_POWER_RESTRICTIONS appop to TestDPC app
- Verify the app can start fg services from the bg
- Verify fgs started by the app cannot be stopped
- Verify the app cannot be put into background restricted via Settings

Change-Id: If9e76076c59195f1e6e5f3eee3c8e7a0c754d8de

tests/unit/src/com/android/settings/applications/AppStateAppBatteryUsageBridgeTest.java

@@ -40,7 +40,7 @@ public final class AppStateAppBatteryUsageBridgeTest {
 
   @Test
   public void updateExtraInfo_updatesRestricted() {
-    when(mPowerAllowlistBackend.isAllowlisted(TEST_PACKAGE_1)).thenReturn(false);
+    when(mPowerAllowlistBackend.isAllowlisted(TEST_PACKAGE_1, UID_1)).thenReturn(false);
     when(mAppOpsManager.checkOpNoThrow(AppOpsManager.OP_RUN_ANY_IN_BACKGROUND,
             UID_1, TEST_PACKAGE_1)).thenReturn(AppOpsManager.MODE_IGNORED);
     AppStateAppBatteryUsageBridge bridge =
@@ -59,7 +59,7 @@ public final class AppStateAppBatteryUsageBridgeTest {
 
   @Test
   public void updateExtraInfo_updatesUnrestricted() {
-    when(mPowerAllowlistBackend.isAllowlisted(TEST_PACKAGE_1)).thenReturn(true);
+    when(mPowerAllowlistBackend.isAllowlisted(TEST_PACKAGE_1, UID_1)).thenReturn(true);
     when(mAppOpsManager.checkOpNoThrow(AppOpsManager.OP_RUN_ANY_IN_BACKGROUND,
             UID_2, TEST_PACKAGE_2)).thenReturn(AppOpsManager.MODE_ALLOWED);
     AppStateAppBatteryUsageBridge bridge =