Fix Avalonia.Controls.ColorPicker.csproj

- Disable ApiDiff tool
- Enable nullable reference types

src/Avalonia.Controls.ColorPicker/Avalonia.Controls.ColorPicker.csproj

@@ -3,6 +3,9 @@
     <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <!--<PackageId>Avalonia.Controls.ColorPicker</PackageId>-->
   </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />
     <ProjectReference Include="..\Avalonia.Remote.Protocol\Avalonia.Remote.Protocol.csproj" />
@@ -16,6 +19,7 @@
   <Import Project="..\..\build\EmbedXaml.props" />
   <Import Project="..\..\build\JetBrains.Annotations.props" />
   <Import Project="..\..\build\BuildTargets.targets" />
-  <Import Project="..\..\build\ApiDiff.props" />
+  <!--<Import Project="..\..\build\ApiDiff.props" />-->
+  <Import Project="..\..\build\NullableEnable.props" />
   <Import Project="..\..\build\DevAnalyzers.props" />
 </Project>