Expose public APIs for Azure plugin to generate ResourceData (#5544)

Expose more public APIs:
- MrwSerializationtypeDefinition to manipulate serialization in
sub-plugin
- TypeFacotry.CreateModelCore to create ResourceData in Azure plugin

The corresponding Azure plugin PR:
Azure/azure-sdk-for-net#47730

Author: live1206

packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT License.
 
 using System;
-using System.ClientModel;
 using System.ClientModel.Primitives;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -26,7 +25,7 @@ namespace Microsoft.Generator.CSharp.ClientModel.Providers
     /// <summary>
     /// This class provides the set of serialization models, methods, and interfaces for a given model.
     /// </summary>
-    internal class MrwSerializationTypeDefinition : TypeProvider
+    public class MrwSerializationTypeDefinition : TypeProvider
     {
         private const string JsonModelWriteCoreMethodName = "JsonModelWriteCore";
         private const string JsonModelCreateCoreMethodName = "JsonModelCreateCore";

packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/TypeFactory.cs

@@ -151,7 +151,7 @@ protected internal TypeFactory()
             return modelProvider;
         }
 
-        private ModelProvider? CreateModelCore(InputModelType model)
+        protected virtual ModelProvider? CreateModelCore(InputModelType model)
         {
             ModelProvider? type = new ModelProvider(model);
             if (Visitors.Count == 0)