Add comments for default namespace in workspace

src/VisualStudio/Core/Def/Implementation/ProjectSystem/Legacy/AbstractLegacyProject.cs

@@ -308,6 +308,9 @@ private static void ComputeFolderNames(uint folderItemID, List<string> names, IV
         /// Get the default namespace of the project ("" if not defined, which means global namespace),
         /// or null if it is unknown or not applicable. 
         /// </summary>
+        /// <remarks>
+        /// This only has meaning in C# and is explicitly set to null in VB.
+        /// </remarks>>
         private static string GetDefaultNamespace(IVsHierarchy hierarchy, string language)
         {
             // While both csproj and vbproj might define <rootnamespace> property in the project file, 

src/Workspaces/Core/MSBuild/MSBuild/ProjectFile/ProjectFileInfo.cs

@@ -39,6 +39,9 @@ internal sealed class ProjectFileInfo
         /// The default namespace of the project ("" if not defined, which means global namespace),
         /// or null if it is unknown or not applicable. 
         /// </summary>
+        /// <remarks>
+        /// This only has meaning in C# and is explicitly set to null in VB.
+        /// </remarks>>
         public string DefaultNamespace { get; }
 
         /// <summary>

src/Workspaces/Core/Portable/Workspace/Solution/Project.cs

@@ -66,6 +66,9 @@ internal Project(Solution solution, ProjectState projectState)
         /// The default namespace of the project ("" if not defined, which means global namespace),
         /// or null if it is unknown or not applicable. 
         /// </summary>
+        /// <remarks>
+        /// This only has meaning in C# and is explicitly set to null in VB.
+        /// </remarks>>
         internal string DefaultNamespace => _projectState.DefaultNamespace;
 
         /// <summary>

src/Workspaces/Core/Portable/Workspace/Solution/ProjectInfo.cs

@@ -62,6 +62,9 @@ public sealed class ProjectInfo
         /// The default namespace of the project ("" if not defined, which means global namespace),
         /// or null if it is unknown or not applicable. 
         /// </summary>
+        /// <remarks>
+        /// This only has meaning in C# and is explicitly set to null in VB.
+        /// </remarks>>
         internal string DefaultNamespace => Attributes.DefaultNamespace;
 
         /// <summary>