Add back in copying of RuntimeAssets during publish.

Any NuGet packages that had contentFiles weren't getting the content files added to the published output directory.  This breaks things like debugging in VS Code.

Fix #2459

src/dotnet/commands/dotnet-publish/PublishCommand.cs

@@ -141,6 +141,7 @@ private bool PublishProjectContext(ProjectContext context, string buildBasePath,
 
                 PublishAssetGroups(export.RuntimeAssemblyGroups, outputPath, nativeSubdirectories: false, includeRuntimeGroups: context.IsPortable);
                 PublishAssetGroups(export.NativeLibraryGroups, outputPath, nativeSubdirectories, includeRuntimeGroups: context.IsPortable);
+                export.RuntimeAssets.StructuredCopyTo(outputPath, outputPaths.IntermediateOutputDirectoryPath);
             }
 
             if (options.PreserveCompilationContext.GetValueOrDefault())