Pack Microsoft.AspNetCore.Components.Gateway (#66579)

Microsoft.NET.Sdk.Web.ProjectSystem.props sets <IsPackable>false</IsPackable> by default. The Gateway project uses the Web SDK with a custom <NuspecFile> and <IsShippingPackage>true</IsShippingPackage>, but Pack silently no-ops
under the Web SDK default, so no shipping nupkg is produced.

Set <IsPackable>true</IsPackable> explicitly so the existing nuspec is honored and Microsoft.AspNetCore.Components.Gateway.<version>.nupkg is produced into artifacts/packages/<config>/Shipping/ alongside the other shipping packages.

Verified locally: before this change, ./eng/build.ps1 -pack -projects ... succeeds with 0 errors but produces no nupkg anywhere under artifacts/. After this change, the same invocation produces both the package and its symbols package in the Shipping folder, with the expected build/ targets and tools/ payload.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: danroth27

src/Components/Gateway/src/Microsoft.AspNetCore.Components.Gateway.csproj

@@ -6,6 +6,9 @@
     <AssemblyName>blazor-gateway</AssemblyName>
     <PackageId>Microsoft.AspNetCore.Components.Gateway</PackageId>
     <IsShippingPackage>true</IsShippingPackage>
+    <!-- Microsoft.NET.Sdk.Web defaults IsPackable to false. Override it so the
+         <NuspecFile> below is honored and the shipping package is produced. -->
+    <IsPackable>true</IsPackable>
     <Description>Gateway server for hosting standalone Blazor WebAssembly applications.</Description>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <!-- Assemblies should not reference this assembly directly -->