C#: Open the solution directory when using VSCode

The solution directory used to be the same as the project
directory (`res://`). We now allow specifying a different
path for the solution and the other external editors already
use that (which seems more convenient for multi-project
scenarios).

modules/mono/editor/GodotTools/GodotTools/GodotSharpEditor.cs

@@ -272,8 +272,7 @@ namespace GodotTools
                         }
                     }
 
-                    string resourcePath = ProjectSettings.GlobalizePath("res://");
-                    args.Add(resourcePath);
+                    args.Add(Path.GetDirectoryName(GodotSharpDirs.ProjectSlnPath));
 
                     string scriptPath = ProjectSettings.GlobalizePath(script.ResourcePath);