MDL-38509 Implement new plugin_manager::plugintype_name()

This has exactly the same behaviour as the existing
plugintype_name_plural() method, but returns the singular form of the
plugin type (such as 'Activity module').

lib/pluginlib.php

@@ -229,6 +229,35 @@ class plugin_manager {
         return $this->pluginsinfo[$type][$name]->displayname;
     }
 
+    /**
+     * Returns a localized name of a plugin typed in singular form
+     *
+     * Most plugin types define their names in core_plugin lang file. In case of subplugins,
+     * we try to ask the parent plugin for the name. In the worst case, we will return
+     * the value of the passed $type parameter.
+     *
+     * @param string $type the type of the plugin, e.g. mod or workshopform
+     * @return string
+     */
+    public function plugintype_name($type) {
+
+        if (get_string_manager()->string_exists('type_' . $type, 'core_plugin')) {
+            // for most plugin types, their names are defined in core_plugin lang file
+            return get_string('type_' . $type, 'core_plugin');
+
+        } else if ($parent = $this->get_parent_of_subplugin($type)) {
+            // if this is a subplugin, try to ask the parent plugin for the name
+            if (get_string_manager()->string_exists('subplugintype_' . $type, $parent)) {
+                return $this->plugin_name($parent) . ' / ' . get_string('subplugintype_' . $type, $parent);
+            } else {
+                return $this->plugin_name($parent) . ' / ' . $type;
+            }
+
+        } else {
+            return $type;
+        }
+    }
+
     /**
      * Returns a localized name of a plugin type in plural form
      *