[PreviewPane] Porting .NET Core 3.1 (#8432)

* PreviewPane porting .NET core 3.1

* Adding in misspellings

Co-authored-by: Clint Rutkas <clint@rutkas.com>

src/modules/previewpane/STATestMethodAttribute.cs

@@ -0,0 +1,55 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+// Used for STA tests in PreviewPane
+namespace Microsoft.PowerToys.STATestExtension
+{
+    public class STATestMethodAttribute : TestMethodAttribute
+    {
+        private readonly TestMethodAttribute _testMethodAttribute;
+
+        public STATestMethodAttribute()
+        {
+        }
+
+        public STATestMethodAttribute(TestMethodAttribute testMethodAttribute)
+        {
+            _testMethodAttribute = testMethodAttribute;
+        }
+
+        public override TestResult[] Execute(ITestMethod testMethod)
+        {
+            if (testMethod == null)
+            {
+                throw new ArgumentNullException(nameof(testMethod));
+            }
+
+            if (Thread.CurrentThread.GetApartmentState() == ApartmentState.STA)
+            {
+                return Invoke(testMethod);
+            }
+
+            TestResult[] result = null;
+            var thread = new Thread(() => result = Invoke(testMethod));
+            thread.SetApartmentState(ApartmentState.STA);
+            thread.Start();
+            thread.Join();
+            return result;
+        }
+
+        private TestResult[] Invoke(ITestMethod testMethod)
+        {
+            if (_testMethodAttribute != null)
+            {
+                return _testMethodAttribute.Execute(testMethod);
+            }
+
+            return new[] { testMethod.Invoke(null) };
+        }
+    }
+}