Update TypeProvider (#5432)

Needed for Azure/azure-sdk-for-net#47665
- Update modifiers of TypeProvider
- Update relativeFilePath of TypeProvdier
- remove sealed from ModelProvider, so that `ResourceDataProvdier` in
Azure plugin can share most of the existing logic

Author: live1206

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

@@ -15,7 +15,7 @@
 
 namespace Microsoft.Generator.CSharp.Providers
 {
-    public sealed class ModelProvider : TypeProvider
+    public class ModelProvider : TypeProvider
     {
         private const string AdditionalBinaryDataPropsFieldDescription = "Keeps track of any properties unknown to the library.";
         private readonly InputModelType _inputModel;

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

@@ -123,11 +123,7 @@ public string? Deprecated
 
         private TypeSignatureModifiers? _declarationModifiers;
 
-        public TypeSignatureModifiers DeclarationModifiers
-        {
-            get => _declarationModifiers ??= GetDeclarationModifiersInternal();
-            private set => _declarationModifiers = value;
-        }
+        public TypeSignatureModifiers DeclarationModifiers => _declarationModifiers ??= GetDeclarationModifiersInternal();
 
         protected virtual TypeSignatureModifiers GetDeclarationModifiers() => TypeSignatureModifiers.None;
 
@@ -332,7 +328,9 @@ public void Update(
             IEnumerable<FieldProvider>? fields = null,
             IEnumerable<TypeProvider>? serializations = null,
             IEnumerable<TypeProvider>? nestedTypes = null,
-            XmlDocProvider? xmlDocs = null)
+            XmlDocProvider? xmlDocs = null,
+            TypeSignatureModifiers? modifiers = null,
+            string? relativeFilePath = null)
         {
             if (methods != null)
             {
@@ -362,6 +360,14 @@ public void Update(
             {
                 XmlDocs = xmlDocs;
             }
+            if (modifiers != null)
+            {
+                _declarationModifiers = modifiers;
+            }
+            if (relativeFilePath != null)
+            {
+                _relativeFilePath = relativeFilePath;
+            }
         }
         public IReadOnlyList<EnumTypeMember> EnumValues => _enumValues ??= BuildEnumValues();