Fixed some compiler warnings.

Author: reduckted

src/toolkit/Community.VisualStudio.Toolkit.Shared/MEF/TokenOutliningTaggerBase.cs

@@ -57,7 +57,7 @@ private static TagSpan<IStructureTag> CreateTag(SnapshotSpan span, string text,
                         guideLineHorizontalAnchor: span.Start,
                         type: PredefinedStructureTagTypes.Structural,
                         isCollapsible: true,
-                        collapsedForm: tag.GetOutliningText(text),
+                        collapsedForm: tag.GetOutliningText!(text),
                         collapsedHintForm: null);
 
             return new TagSpan<IStructureTag>(span, structureTag);

src/toolkit/Community.VisualStudio.Toolkit.Shared/Notifications/RatingPrompt.cs

@@ -125,6 +125,8 @@ private async Task IncrementAsync()
         /// </summary>
         public async Task PromptAsync()
         {
+            await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
+           
             InfoBar? infoBar = await CreateInfoBarAsync();
 
             if (infoBar == null)

src/toolkit/Community.VisualStudio.Toolkit.Shared/Windows/WindowFrame.cs

@@ -231,6 +231,8 @@ public async Task<bool> IsOnScreenAsync()
         /// <returns><see langword="null"/> if the window isn't a document window.</returns>
         public async Task<DocumentView?> GetDocumentViewAsync()
         {
+            await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
+           
             // Force the loading of a document that may be pending initialization.
             // See https://docs.microsoft.com/en-us/visualstudio/extensibility/internals/delayed-document-loading
             _frame.GetProperty((int)__VSFPROPID.VSFPROPID_DocView, out _);