improve userPicker: delegate query to authorization helper

Tests/Security/Authorization/AuthorizationHelperTest.php

@@ -459,6 +459,20 @@ class AuthorizationHelperTest extends KernelTestCase
             "Assert that `CHILL_MASTER_ROLE` is a parent of `CHILL_INHERITED_ROLE_1`");
     }
     
-    
+    public function testFindUsersReaching()
+    {
+        $centerA = static::$kernel->getContainer()
+            ->get('doctrine.orm.entity_manager')
+            ->getRepository(Center::class)
+            ->findOneByName('Center A');
+        
+        $users = $this->getAuthorizationHelper()
+            ->findUsersReaching(new Role('CHILL_PERSON_SEE'), 
+                $centerA);
+        
+        $usernames = \array_map(function(User $u) { return $u->getUsername(); }, $users);
+        
+        $this->assertContains('center a_social', $usernames);
+    }
     
 }