Preserve leading trivia when deleting TestClassAttribute

I noticed diffs of the form:

-    /// <summary>
-    /// Verify the functioning of the BuildErrorEventArg class.
-    /// </summary>
-    [TestClass]

Where not only was the not-needed-in-xunit attribute removed, but its
removal also deleted class-level doc comments.  This change preserves
leading trivia on the deleted AttributeList.  That trivia is normally
blank (so this doesn't break the existing scenario), but a leading comment
or doc comment will be present there.

Author: rainersigwald

src/XUnitConverter.Tests/MSTestToXUnitConverterTests.cs

@@ -103,6 +103,42 @@ public class MyTestClass
             await Verify(text, expected);
         }
 
+        [Fact]
+        public async Task TestPreserveClassDocComments()
+        {
+            string text = @"
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace System.Composition.UnitTests
+{
+    /// <summary>
+    /// Some sort of doc comment.
+    /// </summary>
+    [TestClass]
+    public class MyTestClass
+    {
+    }
+}
+";
+            var expected = @"
+using System;
+using Xunit;
+
+namespace System.Composition.UnitTests
+{
+    /// <summary>
+    /// Some sort of doc comment.
+    /// </summary>
+    public class MyTestClass
+    {
+    }
+}
+";
+            await Verify(text, expected);
+        }
+
+
         [Fact]
         public async Task TestUpdatesTestMethodAttributes()
         {

src/XUnitConverter/MSTestToXUnitConverter.cs

@@ -163,7 +163,7 @@ private void RemoveTestAttributes(CompilationUnitSyntax root, SemanticModel sema
                     }
                     else
                     {
-                        transformationRoot = transformationRoot.RemoveNode(attributeListSyntax, SyntaxRemoveOptions.KeepNoTrivia);
+                        transformationRoot = transformationRoot.RemoveNode(attributeListSyntax, SyntaxRemoveOptions.KeepLeadingTrivia);
                     }
                 }
                 return transformationRoot;