Invalidate project engine when UseRoslynTokenizer changes

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

@@ -151,16 +151,17 @@ internal class ProjectState
         else
         {
             ProjectWorkspaceStateVersion = Version;
-        }
 
-        if ((difference & ClearProjectWorkspaceStateVersionMask) != 0 &&
-            CSharpLanguageVersion != older.CSharpLanguageVersion)
+            // CSharpLanguageVersion and UseRoslynTokenizer are part of the ProjectWorkspaceState, but they affect the project engine
+            // so we check for those specifically changing, and clear that.
+            if (CSharpLanguageVersion != older.CSharpLanguageVersion ||
+                ProjectWorkspaceState.UseRoslynTokenizer != older.ProjectWorkspaceState.UseRoslynTokenizer)
             {
-            // C# language version changed. This impacts the ProjectEngine, reset it.
                 _projectEngine = null;
                 ConfigurationVersion = Version;
             }
         }
+    }
 
     // Internal set for testing.
     public ImmutableDictionary<string, DocumentState> Documents { get; internal set; }