C#: Add missing files

csharp/extractor/Semmle.Util/FileRenamer.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace Semmle.Util
+{
+    /// <summary>
+    /// Utility to temporarily rename a set of files.
+    /// </summary>
+    public sealed class FileRenamer : IDisposable
+    {
+        readonly string[] files;
+        const string suffix = ".codeqlhidden";
+
+        public FileRenamer(IEnumerable<FileInfo> oldFiles)
+        {
+            files = oldFiles.Select(f => f.FullName).ToArray();
+
+            foreach (var file in files)
+            {
+                File.Move(file, file + suffix);
+            }
+        }
+
+        public void Dispose()
+        {
+            foreach (var file in files)
+            {
+                File.Move(file + suffix, file);
+            }
+        }
+    }
+}

csharp/extractor/Semmle.Util/TemporaryDirectory.cs

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+using System;
+using System.IO;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace Semmle.Util
+{
+    /// <summary>
+    /// A temporary directory that is created within the system temp directory.
+    /// When this object is disposed, the directory is deleted.
+    /// </summary>
+    public sealed class TemporaryDirectory : IDisposable
+    {
+        public DirectoryInfo DirInfo { get; }
+
+        public TemporaryDirectory(string name)
+        {
+            DirInfo = new DirectoryInfo(name);
+            DirInfo.Create();
+        }
+
+        public void Dispose()
+        {
+            DirInfo.Delete(true);
+        }
+
+        public override string ToString() => DirInfo.FullName.ToString();
+    }
+}