Permission Check For DPM Get IME API

Require the caller of DPM.getPermittedInputMethodsForCurrentUser() to
hold the MANAGE_USERS permission.  The only callers should be settings
apps which already hold this permission.

Bug: 62343414
Test: Manage IME list in the Settings app
Test: com.google.android.gts.devicepolicy.DeviceOwnerTest#testPermitInputMethods
Change-Id: I0d162f8f51d16e403a950ee5d942502c2cf20181

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

@@ -6340,6 +6340,7 @@ public class DevicePolicyManager {
      * @hide
      */
     @SystemApi
+    @RequiresPermission(android.Manifest.permission.MANAGE_USERS)
     public @Nullable List<String> getPermittedInputMethodsForCurrentUser() {
         throwIfParentInstance("getPermittedInputMethodsForCurrentUser");
         if (mService != null) {

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

@@ -8738,6 +8738,7 @@ public class DevicePolicyManagerService extends BaseIDevicePolicyManager {
 
     @Override
     public List getPermittedInputMethodsForCurrentUser() {
+        enforceManageUsers();
         UserInfo currentUser;
         try {
             currentUser = mInjector.getIActivityManager().getCurrentUser();