Yield in task continuation to prevent stack overflow (#78902)

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2428510

Author: CyrusNajmabadi

src/EditorFeatures/Core/IntelliSense/ModelComputation.cs

@@ -146,8 +146,10 @@ public void ChainTaskAndNotifyControllerWhenFinished(
 
         async Task<TModel> TransformModelAsync(Task<TModel> lastTask)
         {
-            // Ensure we're on the BG before doing any model transformation work.
-            await TaskScheduler.Default;
+            // Ensure we're on the BG before doing any model transformation work. Also, ensure we yield so that we don't
+            // end up with an enormously long chain of tasks unwinding.  That can otherwise cause a stack overflow if
+            // this chain gets too long.
+            await Task.Yield().ConfigureAwait(false);
             var model = await lastTask.ConfigureAwait(false);
             return await transformModelAsync(model, _stopCancellationToken).ConfigureAwait(false);
         }