Shared EvaluationContext for graph construction

Fix dotnet#9678 by creating a single shared `EvaluationContext` in the `Graph`
object and using it when creating `ProjectInstance`s using the default
factory.

This is similar to how NuGet static-graph restore already works: https://github.com/NuGet/NuGet.Client/blob/b83566ec2369c4e9fd07e6f95d734dfe370a1e66/src/NuGet.Core/NuGet.Build.Tasks.Console/MSBuildStaticGraphRestore.cs#L885

Since we're evaluating the projects in the graph in parallel and "all at
once", the shared caches in the `EvaluationContext` should be a solid
improvement.

src/Build.UnitTests/Graph/ProjectGraph_Tests.cs

@@ -9,6 +9,7 @@
 using System.Text.RegularExpressions;
 using Microsoft.Build.Construction;
 using Microsoft.Build.Evaluation;
+using Microsoft.Build.Evaluation.Context;
 using Microsoft.Build.Exceptions;
 using Microsoft.Build.Execution;
 using Microsoft.Build.Framework;
@@ -107,10 +108,11 @@ public void ConstructWithSingleNodeWithProjectInstanceFactory()
                     (projectPath, globalProperties, projectCollection) =>
                     {
                         factoryCalled = true;
-                        return ProjectGraph.DefaultProjectInstanceFactory(
+                        return ProjectGraph.StaticProjectInstanceFactory(
                             projectPath,
                             globalProperties,
-                            projectCollection);
+                            projectCollection,
+                            EvaluationContext.Create(EvaluationContext.SharingPolicy.Isolated));
                     });
                 projectGraph.ProjectNodes.Count.ShouldBe(1);
                 projectGraph.ProjectNodes.First().ProjectInstance.FullPath.ShouldBe(entryProject.Path);

src/Build/Graph/ProjectGraph.cs

@@ -11,6 +11,7 @@
 using System.Text;
 using System.Threading;
 using Microsoft.Build.Evaluation;
+using Microsoft.Build.Evaluation.Context;
 using Microsoft.Build.Eventing;
 using Microsoft.Build.Exceptions;
 using Microsoft.Build.Execution;
@@ -56,6 +57,8 @@ public sealed class ProjectGraph
 
         private readonly Lazy<IReadOnlyCollection<ProjectGraphNode>> _projectNodesTopologicallySorted;
 
+        private readonly EvaluationContext _evaluationContext = EvaluationContext.Create(EvaluationContext.SharingPolicy.Shared);
+
         private GraphBuilder.GraphEdges Edges { get; }
 
         internal GraphBuilder.GraphEdges TestOnly_Edges => Edges;
@@ -742,16 +745,31 @@ private static ImmutableList<string> ExpandDefaultTargets(ImmutableList<string>
             return targets;
         }
 
-        internal static ProjectInstance DefaultProjectInstanceFactory(
+        internal ProjectInstance DefaultProjectInstanceFactory(
             string projectPath,
             Dictionary<string, string> globalProperties,
             ProjectCollection projectCollection)
+        {
+            return StaticProjectInstanceFactory(
+                                projectPath,
+                                globalProperties,
+                                projectCollection,
+                                _evaluationContext);
+        }
+
+        internal static ProjectInstance StaticProjectInstanceFactory(
+            string projectPath,
+            Dictionary<string, string> globalProperties,
+            ProjectCollection projectCollection,
+            EvaluationContext evaluationContext)
         {
             return new ProjectInstance(
                 projectPath,
                 globalProperties,
                 MSBuildConstants.CurrentToolsVersion,
-                projectCollection);
+                subToolsetVersion: null,
+                projectCollection,
+                evaluationContext);
         }
 
         private struct ProjectGraphBuildRequest : IEquatable<ProjectGraphBuildRequest>

src/Build/Instance/ProjectInstance.cs

@@ -248,6 +248,11 @@ public ProjectInstance(string projectFile, IDictionary<string, string> globalPro
         {
         }
 
+        public ProjectInstance(string projectFile, IDictionary<string, string> globalProperties, string toolsVersion, string subToolsetVersion, ProjectCollection projectCollection, EvaluationContext context, bool interactive = false)
+            : this(projectFile, globalProperties, toolsVersion, subToolsetVersion, projectCollection, projectLoadSettings: null, evaluationContext: context, directoryCacheFactory: null, interactive: false)
+        {
+        }
+
         /// <summary>
         /// Creates a ProjectInstance directly.
         /// No intermediate Project object is created.