Allow NuGet.org for CShells packages

Map CShells package IDs to NuGet.org as well as the CShells Feedz source so solution restore can resolve published CShells packages when the Feedz source has no matching package.

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

NuGet.Config

@@ -11,6 +11,8 @@
     <packageSourceMapping>
         <packageSource key="NuGet official package source">
             <package pattern="*" />
+            <package pattern="CShells" />
+            <package pattern="CShells.*" />
         </packageSource>
         <packageSource key="cshells-feedz">
             <package pattern="CShells" />