Merge pull request #10542 from jmarolf/stabilization

Do not throw if initialized by Winforms UI thread
Fixes https://github.com/dotnet/roslyn/issues/10510

src/Workspaces/Core/Portable/Utilities/ForegroundThreadDataKind.cs

@@ -13,6 +13,7 @@ namespace Microsoft.CodeAnalysis.Utilities
     internal enum ForegroundThreadDataKind
     {
         Wpf,
+        WinForms,
         StaUnitTest,
         JoinableTask,
         ForcedByPackageInitialize,
@@ -43,6 +44,10 @@ internal static ForegroundThreadDataKind CreateDefault(ForegroundThreadDataKind
 
                     return JoinableTask;
 
+                case "System.Windows.Forms.WindowsFormsSynchronizationContext":
+
+                    return WinForms;
+
                 default:
 
                     return defaultKind;