Further clean up and organization in ProjectSnapshotManager

Author: DustinCampbell

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/IProjectSnapshotManager.cs

@@ -14,6 +14,8 @@ internal interface IProjectSnapshotManager
     event EventHandler<ProjectChangeEventArgs> PriorityChanged;
     event EventHandler<ProjectChangeEventArgs> Changed;
 
+    bool IsSolutionClosing { get; }
+
     ImmutableArray<ProjectKey> GetAllProjectKeys(string projectFileName);
     ImmutableArray<IProjectSnapshot> GetProjects();
     IProjectSnapshot GetLoadedProject(ProjectKey projectKey);

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectSnapshotManager.Entry.cs

@@ -0,0 +1,17 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+namespace Microsoft.CodeAnalysis.Razor.ProjectSystem;
+
+internal partial class ProjectSnapshotManager
+{
+    private sealed record Entry(ProjectState State)
+    {
+        private IProjectSnapshot? _snapshotUnsafe;
+
+        public IProjectSnapshot GetSnapshot()
+        {
+            return _snapshotUnsafe ??= new ProjectSnapshot(State);
+        }
+    }
+}