Almost all of the code to prime the NuGet cache from the archive.

- Created a Configurer class that is responsible for deciding when to run the dotnet first time use
experience and invoke the NuGetCachePrimer.
- Added the NuGetCachePrimer which extract the archive and primes the cache.
-- This is just missing creating the sentinel once restore succeeds.
- Added a shell for the NugetPackagesArchiver, which will be responsible for expanding the archive (likely
replaced in the future by an abstraction from Eric's code or its implementation will simply call Eric's code).
- Added a TemporaryFolder abstration to Internal Abstractions that handles deleting the temporary folder once
we are done with it.

test/Microsoft.DotNet.Configurer.UnitTests/GivenADotnetFirstTimeUseConfigurer.cs

@@ -0,0 +1,69 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using FluentAssertions;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.Configurer;
+using Microsoft.DotNet.Tools.Test;
+using Microsoft.Extensions.DependencyModel.Tests;
+using Microsoft.Extensions.EnvironmentAbstractions;
+using Moq;
+using Xunit;
+
+namespace Microsoft.DotNet.Configurer.UnitTests
+{
+    public class GivenADotnetFirstTimeUseConfigurer
+    {
+        private const string NUGET_CACHE_PATH = "some path";
+
+        private Mock<INuGetCachePrimer> _nugetCachePrimerMock;
+        private Mock<INuGetCacheResolver> _nugetCacheResolverMock;
+
+        public GivenADotnetFirstTimeUseConfigurer()
+        {
+            _nugetCachePrimerMock = new Mock<INuGetCachePrimer>();
+            _nugetCacheResolverMock = new Mock<INuGetCacheResolver>();
+            _nugetCacheResolverMock.Setup(n => n.ResolveNugetCachePath()).Returns(NUGET_CACHE_PATH);
+        }
+
+        [Fact]
+        public void The_sentinel_has_the_current_version_in_its_name()
+        {
+            DotnetFirstTimeUseConfigurer.SENTINEL.Should().Contain($"{Product.Version}");
+        }
+
+        [Fact]
+        public void It_does_not_prime_the_cache_if_the_sentinel_exists()
+        {
+            var fileSystemMockBuilder = FileSystemMockBuilder.Create();
+            fileSystemMockBuilder.AddFiles(NUGET_CACHE_PATH, DotnetFirstTimeUseConfigurer.SENTINEL);
+
+            var fileSystemMock = fileSystemMockBuilder.Build();
+
+            var dotnetFirstTimeUseConfigurer = new DotnetFirstTimeUseConfigurer(
+                _nugetCachePrimerMock.Object,
+                _nugetCacheResolverMock.Object,
+                fileSystemMock.File);
+
+            dotnetFirstTimeUseConfigurer.Configure();
+
+            _nugetCachePrimerMock.Verify(r => r.PrimeCache(), Times.Never);
+        }
+
+        [Fact]
+        public void It_primes_the_cache_if_the_sentinel_does_not_exist()
+        {
+            var fileSystemMockBuilder = FileSystemMockBuilder.Create();
+            var fileSystemMock = fileSystemMockBuilder.Build();
+
+            var dotnetFirstTimeUseConfigurer = new DotnetFirstTimeUseConfigurer(
+                _nugetCachePrimerMock.Object,
+                _nugetCacheResolverMock.Object,
+                fileSystemMock.File);
+
+            dotnetFirstTimeUseConfigurer.Configure();
+
+            _nugetCachePrimerMock.Verify(r => r.PrimeCache(), Times.Once);
+        }
+    }
+}