feat: Enhance MegaMenu with localization, caching, and new properties

- Added localization support for loading states, empty navigation, and submenu actions in both German and English.
- Introduced new properties in IMenuItem for description, openInNewWindow, and external links.
- Updated SPTermStorePickerService to handle cache versioning and language-specific caching.
- Implemented a new MegaMenuCore service for handling term properties, cache management, and navigation URL resolution.
- Refactored TaxonomyNavigationService to build menu hierarchy and filter hidden terms.
- Added automated tests for MegaMenu core functionalities and static asset validation.
- Removed unused ItemDictionary service.
- Created a comprehensive ToDo document outlining the implementation status and future tasks.

tests/validate-static-assets.js

@@ -0,0 +1,44 @@
+'use strict';
+
+var fs = require('fs');
+
+function assert(name, condition) {
+    if (!condition) {
+        throw new Error('FAILED: ' + name);
+    }
+    console.log('OK:', name);
+}
+
+function read(path) {
+    return fs.readFileSync(path, 'utf8');
+}
+
+function validatePreview(path) {
+    var html = read(path);
+    var start = html.indexOf('<script>');
+    var end = html.indexOf('</script>', start);
+    assert(path + ' contains script', start >= 0 && end > start);
+    new Function(html.substring(start + 8, end));
+    assert(path + ' script syntax', true);
+    assert(path + ' uses production CSS', html.indexOf('../classic/megamenu-classic.css') >= 0);
+    assert(path + ' has mobile toggle', html.indexOf('mega-menu-mobile-toggle') >= 0);
+    assert(path + ' has accessible submenu toggle', html.indexOf('menu-item-toggle') >= 0 && html.indexOf('aria-controls') >= 0);
+}
+
+function validateStyle(path) {
+    var css = read(path);
+    var opening = (css.match(/\{/g) || []).length;
+    var closing = (css.match(/\}/g) || []).length;
+    assert(path + ' balanced blocks', opening === closing);
+    ['mega-menu-mobile-toggle', 'menu-item-toggle', 'flyout-toggle', 'mega-menu-description'].forEach(function (className) {
+        assert(path + ' contains ' + className, css.indexOf(className) >= 0);
+    });
+}
+
+validatePreview('preview/mega-menu-preview.html');
+validatePreview('preview/flyout-menu-preview.html');
+validateStyle('classic/megamenu-classic.css');
+validateStyle('src/extensions/megaMenu/MegaMenu.module.scss');
+
+console.log('Static MegaMenu asset tests passed.');
+