MDL-50887 antivirus: clamav is standard plugin, missing strings

lang/en/plugin.php

@@ -105,6 +105,8 @@ $string['status_upgrade'] = 'To be upgraded';
 $string['status_uptodate'] = 'Installed';
 $string['supportedmoodleversions'] = 'Supported Moodle versions';
 $string['systemname'] = 'Identifier';
+$string['type_antivirus'] = 'Antivirus plugin';
+$string['type_antivirus_plural'] = 'Antivirus plugins';
 $string['type_auth'] = 'Authentication method';
 $string['type_auth_plural'] = 'Authentication methods';
 $string['type_availability'] = 'Availability restriction';

lib/classes/plugin_manager.php

@@ -1684,6 +1684,10 @@ class core_plugin_manager {
 
         $standard_plugins = array(
 
+            'antivirus' => array(
+                'clamav'
+            ),
+
             'atto' => array(
                 'accessibilitychecker', 'accessibilityhelper', 'align',
                 'backcolor', 'bold', 'charmap', 'clear', 'collapse', 'emoticon',