MDL-38509 Implement new plugin_manager::get_plugin_types()

This new method just takes the result of the core get_plugin_types() and
re-orders the plugin types in the same way as they are displayed at the
Plugins overview screen.

lib/pluginlib.php

@@ -96,6 +96,17 @@ class plugin_manager {
         }
     }
 
+    /**
+     * Returns the result of {@link get_plugin_types()} ordered for humans
+     *
+     * @see self::reorder_plugin_types()
+     * @param bool $fullpaths false means relative paths from dirroot
+     * @return array (string)name => (string)location
+     */
+    public function get_plugin_types($fullpaths = true) {
+        return $this->reorder_plugin_types(get_plugin_types($fullpaths));
+    }
+
     /**
      * Returns a tree of known plugins and information about them
      *
@@ -119,8 +130,7 @@ class plugin_manager {
                 }
             }
             $this->pluginsinfo = array();
-            $plugintypes = get_plugin_types();
-            $plugintypes = $this->reorder_plugin_types($plugintypes);
+            $plugintypes = $this->get_plugin_types();
             foreach ($plugintypes as $plugintype => $plugintyperootdir) {
                 if (in_array($plugintype, array('base', 'general'))) {
                     throw new coding_exception('Illegal usage of reserved word for plugin type');