Prepare infrastructure for System.ClientModel 1.6.0-alpha version

Co-authored-by: m-nash <[email protected]>

Author: Copilot

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

@@ -55,7 +55,8 @@ protected override FormattableString BuildDescription()
         private readonly bool _isAbstract;
 
         private readonly CSharpType _additionalBinaryDataPropsFieldType = typeof(IDictionary<string, BinaryData>);
-        private readonly CSharpType _additionalPropertiesType = new CSharpType(typeof(object)); // TODO: Replace with AdditionalProperties when available
+        // TODO: Replace with typeof(System.ClientModel.Primitives.AdditionalProperties) when System.ClientModel 1.6.0-alpha.20250804.4 becomes available
+        private readonly CSharpType _additionalPropertiesType = new CSharpType(typeof(object));
         private readonly Type _additionalPropsUnknownType = typeof(BinaryData);
         private readonly Lazy<TypeProvider?>? _baseTypeProvider;
         private FieldProvider? _rawDataField;

packages/http-client-csharp/generator/NuGet.Config

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
+    <add key="azure-sdk-for-net" value="https://pkgs.dev.azure.com/azure-sdk/public/_packaging/azure-sdk-for-net/nuget/v3/index.json" />
+  </packageSources>
+  <disabledPackageSources>
+    <clear />
+  </disabledPackageSources>
+</configuration>

packages/http-client-csharp/generator/Packages.Data.props

@@ -14,6 +14,7 @@
     <PackageReference Update="NuGet.Versioning" Version="6.14.0" />
     <PackageReference Update="NuGet.Protocol" Version="6.14.0" />
     <PackageReference Update="System.ComponentModel.Composition" Version="8.0.0" />
+    <!-- TODO: Update to 1.6.0-alpha.20250804.4 when available from azure-sdk-for-net feed -->
     <PackageReference Update="System.ClientModel" Version="1.5.1" />
     <PackageReference Update="System.Memory.Data" Version="8.0.1" />
   </ItemGroup>