MDL-67063 h5p: new h5plib plugintype for supporting multi coreAPI

A new plugintype has been created for having more than one installed
third-party H5P libraries. Existing libraries have been moved from
lib/h5p to the new h5plib_v124 plugin.

lib/adminlib.php

@@ -11208,3 +11208,44 @@ class admin_setting_configthemepreset extends admin_setting_configselect {
         return true;
     }
 }
+
+/**
+ * Selection of plugins that can work as H5P libraries handlers
+ *
+ * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @copyright 2020 Sara Arjona <sara@moodle.com>
+ */
+class admin_settings_h5plib_handler_select extends admin_setting_configselect {
+
+    /**
+     * Constructor
+     * @param string $name unique ascii name, either 'mysetting' for settings that in config, or 'myplugin/mysetting'
+     *        for ones in config_plugins.
+     * @param string $visiblename localised
+     * @param string $description long localised info
+     * @param string $defaultsetting
+     */
+    public function __construct($name, $visiblename, $description, $defaultsetting = '') {
+        parent::__construct($name, $visiblename, $description, $defaultsetting, null);
+    }
+
+    /**
+     * Lazy-load the available choices for the select box
+     */
+    public function load_choices() {
+        if (during_initial_install()) {
+            return false;
+        }
+        if (is_array($this->choices)) {
+            return true;
+        }
+
+        $this->choices = \core_h5p\local\library\autoloader::get_all_handlers();
+        foreach ($this->choices as $name => $class) {
+            $this->choices[$name] = new lang_string('sitepolicyhandlerplugin', 'core_admin',
+                ['name' => new lang_string('pluginname', $name), 'component' => $name]);
+        }
+
+        return true;
+    }
+}