MDL-65893 webservice: format site name (handle language tags etc.)

Allow web service clients (like the Moodle App) to benefit from a
formatted (filtered) site name. Select the filtered (localized etc.)
string on server side, before it is sent to the web service client.

For example, this translates a site name which uses language tags in
curly braces when using the filter_multilang2 plugin.

Thanks-To: Juan Leyva <[email protected]>
Thanks-To: Kathrin Osswald <[email protected]>

webservice/externallib.php

@@ -77,6 +77,7 @@ class core_webservice_external extends external_api {
                       array('serviceshortnames'=>$serviceshortnames));
 
         $context = context_user::instance($USER->id);
+        $systemcontext = context_system::instance();
 
         $userpicture = new user_picture($USER);
         $userpicture->size = 1; // Size f1.
@@ -84,7 +85,7 @@ class core_webservice_external extends external_api {
 
         // Site information.
         $siteinfo =  array(
-            'sitename' => $SITE->fullname,
+            'sitename' => external_format_string($SITE->fullname, $systemcontext),
             'siteurl' => $CFG->wwwroot,
             'username' => $USER->username,
             'firstname' => $USER->firstname,