MDL-75078 editor_tiny: Hola TinyMCE 6

Part of MDL-75966

This commit adds TinyMCE version 6.1 into Moodle core.

A basic editor implementation is included, along with Moodle loader, and
basic Plugin API for Moodle. The Plugin API will be extended and
improved in future changes.

A new subplugin is defined for this plugin.

lib/editor/tiny/classes/plugin_with_configuration.php

@@ -0,0 +1,42 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+namespace editor_tiny;
+
+use context;
+
+/**
+ * An interface representing a plugin with menu items.
+ *
+ * @package    editor_tiny
+ * @copyright  2021 Andrew Lyons <[email protected]>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+interface plugin_with_configuration {
+    /**
+     * Get a list of the menu items provided by this plugin.
+     *
+     * @param context $context The context that the editor is used within
+     * @param array $options The options passed in when requesting the editor
+     * @param array $fpoptions The filepicker options passed in when requesting the editor
+     * @return array
+     */
+    public static function get_plugin_configuration_for_context(
+        context $context,
+        array $options,
+        array $fpoptions
+    ): array;
+}