Add usings

Author: captainsafia

src/Http/Http/perf/Microbenchmarks/RequestDelegateGeneratorBenchmarks.cs

@@ -1,7 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
+using System.Text;
 using BenchmarkDotNet.Attributes;
 using Microsoft.AspNetCore.Http.Generators.Tests;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.AspNetCore.Http.Microbenchmarks;