Add CsWinRT1028 suppression

Author: Arlodotexe

Directory.Build.props

@@ -13,6 +13,15 @@
     <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <NoWarn>$(NoWarn);Uno0001</NoWarn>
+    <!--
+      Suppress 'error CsWinRT1028: Class implements WinRT interfaces but isn't marked partial. ' for generated XamlMetaDataProvider.g.cs.
+      Fix is expected to arrive in prerelease1 of Microsoft.WindowsAppSdk 1.6.
+      Internal tracking: https://microsoft.visualstudio.com/OS/_workitems/edit/52541822/
+
+      Notice: This suppression affects CsWinRT1028 for all generated and non-generated code.
+        Disable to check non-generated code for CsWinRT1028.
+     -->
+    <NoWarn>$(NoWarn);CsWinRT1028;</NoWarn>    
   </PropertyGroup>
 
   <Import Project="Windows.Toolkit.Common.props" />