Finish converting 'Prepare' to MSBuild.

Implement DownloadHostAndSharedFxArtifacts
Implement ZipTemplates
Switch the Prepare target to use all the MSBuild targets.

build_projects/dotnet-cli-build/ExtractArchive.cs

@@ -0,0 +1,35 @@
+using System.IO.Compression;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using Microsoft.DotNet.Cli.Build.Framework;
+using static Microsoft.DotNet.Cli.Build.Framework.BuildHelpers;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class ExtractArchive : Task
+    {
+        [Required]
+        public string InputFile { get; set; }
+
+        [Required]
+        public string DestinationDirectory { get; set; }
+
+        public override bool Execute()
+        {
+            FS.Mkdirp(DestinationDirectory);
+
+            Log.LogMessage($"Extracting Archive '{InputFile}' to '{DestinationDirectory}'");
+
+            if (CurrentPlatform.IsWindows)
+            {
+                ZipFile.ExtractToDirectory(InputFile, DestinationDirectory);
+            }
+            else
+            {
+                Exec("tar", "xf", InputFile, "-C", DestinationDirectory);
+            }
+
+            return true;
+        }
+    }
+}