MDL-78613 TinyMCE: Add source code formatting and styling

Add code formatting (indenting) as well as code style (tag color)
via a TinyMC plugin. To make it easier to make code edits when
viewing the editor content in source code view.

lib/editor/tiny/plugins/html/amd/src/common.js

@@ -0,0 +1,41 @@
+// This file is part of Moodle - https://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 <https://www.gnu.org/licenses/>.
+
+/**
+ * Common values helper for the Moodle tiny_html plugin.
+ *
+ * @module      tiny_html/common
+ * @copyright   2023 Matt Porritt <[email protected]>
+ * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+const component = 'tiny_html';
+
+export default {
+    component,
+    pluginName: `${component}/plugin`,
+    codeMirrorStyle: `
+                  .modal-codemirror-container {
+                    position: absolute;
+                    top: 40px;
+                    bottom: 50px;
+                    left: 15px;
+                    right: 15px;
+                    overflow: scroll;
+                    border: 1px solid #c7cace;
+                    border-radius: 5px;
+                  }
+                `
+};