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.

deployment/add-megamenu.ps1

@@ -9,6 +9,8 @@ param(
     [ValidateRange(1, 1440)]
     [int]$CacheMinutes = 15,
 
+    [string]$CacheVersion = '1',
+
     [ValidateSet('megaMenu', 'flyout')]
     [string]$MenuMode = 'megaMenu',
 
@@ -41,6 +43,7 @@ $properties = [string](@{
     termSetName = $TermSetName.Trim()
     termSetId = $TermSetId.Trim()
     cacheMinutes = $CacheMinutes
+    cacheVersion = $CacheVersion
     menuMode = $MenuMode
     debug = [bool]$EnableDebug.IsPresent
 } | ConvertTo-Json -Depth 10 -Compress)