The spawn_helper_process method was introduced together with
get_paths_for_helper_process but was only ever used briefly to spawn
WebContent. Other helper processes (SqlServer, headless_browser etc)
are either execed or spawned with their own helpers & custom arguments.
Currently, we only look at the relative path `./{helper}/{helper}`,
which fails if the working directory is not the same as the directory
where the ladybird binary lives.
