refactor: 使用哈希集合

Author: ArgoZhang

src/components/BootstrapBlazor.Region/Services/DefaultRegionService.cs

@@ -142,11 +142,7 @@ private static void LoadCityData()
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static string Trim(string segment) => segment.Replace("\"", string.Empty).Trim();
 
-#if NET9_0_OR_GREATER
-    private static readonly FrozenSet<string> Provinces =
-#else
     private static readonly HashSet<string> Provinces =
-#endif
     [
         "北京市",
         "天津市",