An editor-only static class that adds a menu item under Editor -> Performant Terrain Scatterer/My Menu Option. When selected it shows an editor dialog saying "It worked!" and a message that the call came from the library's editor code.
using Editor;
public static class MyEditorMenu
{
[Menu( "Editor", "Performant Terrain Scatterer/My Menu Option" )]
public static void OpenMyMenu()
{
EditorUtility.DisplayDialog( "It worked!", "This is being called from your library's editor code!" );
}
}