Permission Check For DPM.getPermittedAccessibilityServices

Require the callers of DPM.getPermittedAccessibilityServices(userId) to
hold the MANAGE_USERS permission.  The only known callers of this API
are settings apps that already hold this permission.

Bug: 62343414
Test: com.android.server.devicepolicy.DevicePolicyManagerTest
Test: com.google.android.gts.devicepolicy.DeviceOwnerTest
Test: Manually checked accessibility settings in DO and PO modes
Change-Id: I8ee3f876fcaffa63636645f0f59709cd147254ef

core/java/android/app/admin/DevicePolicyManager.java

@@ -6198,6 +6198,7 @@ public class DevicePolicyManager {
      * @hide
      */
      @SystemApi
+     @RequiresPermission(android.Manifest.permission.MANAGE_USERS)
      public @Nullable List<String> getPermittedAccessibilityServices(int userId) {
         throwIfParentInstance("getPermittedAccessibilityServices");
         if (mService != null) {

services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java

@@ -8481,6 +8481,7 @@ public class DevicePolicyManagerService extends BaseIDevicePolicyManager {
         if (!mHasFeature) {
             return null;
         }
+        enforceManageUsers();
         synchronized (getLockObject()) {
             List<String> result = null;
             // If we have multiple profiles we return the intersection of the