Include async interfaces in vsix (needed for vs2026 at least)

Author: GrahamTheCoder

Vsix/Vsix.csproj

@@ -51,6 +51,9 @@
   </PropertyGroup>
   <ItemGroup>
     <!-- Build against VS 16.10 -->
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces">
+      <Version>10.0.2</Version>
+    </PackageReference>
     <PackageReference Include="Microsoft.VisualStudio.LanguageServices" Version="4.14.0" />
     <PackageReference Include="Microsoft.VisualStudio.SDK" Version="16.10.31321.278" ExcludeAssets="runtime">
       <IncludeAssets>compile; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>