Make ShapeTables created by PerTenantShapeTableManager frozen

to match DefaultShapeTableManager where this change was made in PR OrchardCMS/OrchardCore#15651.

Lombiq.HelpfulLibraries.OrchardCore/Shapes/PerTenantShapeTableManager.cs

@@ -10,6 +10,7 @@
 using OrchardCore.Settings;
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
@@ -124,8 +125,8 @@ public async Task<ShapeTable> GetShapeTableAsync(string themeId)
             .ToList();
 
         shapeTable = new ShapeTable(
-            descriptors: descriptors.ToDictionary(sd => sd.ShapeType, x => (ShapeDescriptor)x, StringComparer.OrdinalIgnoreCase),
-            bindings: descriptors.SelectMany(sd => sd.Bindings).ToDictionary(kv => kv.Key, kv => kv.Value, StringComparer.OrdinalIgnoreCase)
+            descriptors: descriptors.ToFrozenDictionary(sd => sd.ShapeType, x => (ShapeDescriptor)x, StringComparer.OrdinalIgnoreCase),
+            bindings: descriptors.SelectMany(sd => sd.Bindings).ToFrozenDictionary(kv => kv.Key, kv => kv.Value, StringComparer.OrdinalIgnoreCase)
         );
 
         if (_logger.IsEnabled(LogLevel.Information))