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.

src/extensions/megaMenu/MegaMenuApplicationCustomizer.ts

@@ -28,6 +28,7 @@ export interface IMegaMenuApplicationCustomizerProperties {
   cacheMinutes?: number;
   debug?: boolean;
   menuMode?: MegaMenuMode;
+  cacheVersion?: string;
 }
 
 export default class MegaMenuApplicationCustomizer
@@ -42,7 +43,7 @@ export default class MegaMenuApplicationCustomizer
     const debug: boolean = this._isDebugEnabled();
     debugLog(debug, LOG_SOURCE, 'onInit started.', {
       componentId: UserCustomActionMegaMenuId,
-      version: '2.1.0',
+      version: '2.2.0',
       properties: this.properties || {},
       pageUrl: window.location.href,
       webUrl: this.context.pageContext.web.absoluteUrl,
@@ -108,13 +109,16 @@ export default class MegaMenuApplicationCustomizer
       return;
     }
 
+    this._renderStatus(strings.Loading);
     try {
       debugLog(debug, LOG_SOURCE, 'Creating TaxonomyNavigationService.');
       const taxonomyService: TaxonomyNavigationService = new TaxonomyNavigationService(
         this.context,
         termSetIdentifier,
         debug,
-        this._getCacheMinutes()
+        this._getCacheMinutes(),
+        this._getCacheVersion(),
+        this._getLanguageLcid()
       );
 
       debugLog(debug, LOG_SOURCE, 'Requesting navigation items from taxonomy.');
@@ -123,6 +127,11 @@ export default class MegaMenuApplicationCustomizer
         topLevelItemCount: menuItems.length
       });
 
+      if (!menuItems || menuItems.length === 0) {
+        this._renderStatus(strings.EmptyNavigation);
+        return;
+      }
+
       if (this._renderer) {
         debugLog(debug, LOG_SOURCE, 'Disposing the previous renderer instance.');
         this._renderer.dispose();
@@ -131,7 +140,18 @@ export default class MegaMenuApplicationCustomizer
       this._renderer = new MegaMenuRenderer(
         menuItems,
         debug,
-        this._getMenuMode()
+        this._getMenuMode(),
+        {
+          navigationLabel: strings.NavigationLabel,
+          openNavigation: strings.OpenNavigation,
+          closeNavigation: strings.CloseNavigation,
+          openSubmenu: strings.OpenSubmenu,
+          closeSubmenu: strings.CloseSubmenu,
+          submenuLabel: strings.SubmenuLabel,
+          externalLink: strings.ExternalLink,
+          opened: strings.Opened,
+          closed: strings.Closed
+        }
       );
 
       this._menuContainer = this._getOrCreateContainer('CustomHeader', this._topPlaceholder);
@@ -213,6 +233,19 @@ export default class MegaMenuApplicationCustomizer
     return normalizeMegaMenuMode(this.properties && this.properties.menuMode);
   }
 
+  private _getCacheVersion(): string {
+    const value: string = this.properties && this.properties.cacheVersion
+      ? String(this.properties.cacheVersion).trim()
+      : '1';
+    return value || '1';
+  }
+
+  private _getLanguageLcid(): number {
+    const legacyContext: any = (this.context.pageContext as any).legacyPageContext; // tslint:disable-line:no-any
+    const value: number = legacyContext ? Number(legacyContext.currentLanguage) : 0;
+    return isFinite(value) && value > 0 ? value : 1033;
+  }
+
   private _renderStatus(message: string): void {
     if (!this._topPlaceholder) {
       return;