Use shorter output paths to avoid max path issues on Windows

For example, "out/2" instead of "artifacts/stage2"

.gitignore

@@ -96,6 +96,7 @@ dlldata.c
 # DNX
 project.lock.json
 artifacts/
+out/
 
 *_i.c
 *_p.c

build/OutputDirectories.props

@@ -6,7 +6,7 @@
       <!-- BaseOutputDirectory is the root output path for this stage and RID
            BaseOutputPath is the project-specific output folder that each project builds into.
            This is not confusing at all. -->
-      <BaseOutputDirectory>$(RepoRoot)/artifacts/stage$(CliBuildStage)/$(Rid)</BaseOutputDirectory>
+      <BaseOutputDirectory>$(RepoRoot)/out/$(CliBuildStage)/$(Rid)</BaseOutputDirectory>
       <BaseOutputPath>$([System.IO.Path]::GetFullPath('$(BaseOutputDirectory)/bin/$(MSBuildProjectName)'))</BaseOutputPath>
 
       <BaseIntermediateOutputPath>$([System.IO.Path]::GetFullPath('$(BaseOutputDirectory)/obj/$(MSBuildProjectName)'))</BaseIntermediateOutputPath>

test/Microsoft.DotNet.Tools.Tests.Utilities/RepoDirectoriesProvider.cs

@@ -99,7 +99,10 @@ public RepoDirectoriesProvider(
             string corehostDummyPackages = null,
             string pjDotnet = null)
         {
-            _artifacts = artifacts ?? Path.Combine(RepoRoot, "artifacts", "stage2", BuildRid);
+            _artifacts = artifacts ?? Path.Combine(RepoRoot,
+                                                   "out",
+                                                   "2",     //  Stage - ideally this would come from the CliBuildStage MSBuild property
+                                                   BuildRid);
             _builtDotnet = builtDotnet ?? Path.Combine(_artifacts, "intermediate", "sharedFrameworkPublish");
             _nugetPackages = nugetPackages ?? Path.Combine(RepoRoot, ".nuget", "packages");
             _pjDotnet = pjDotnet ?? GetPjDotnetPath();