lib, test: add duplicate symbol checking in E()

Add duplicate symbol checking in E() to avoid potential confusing
result. Increase coverage of internal/errors.

PR-URL: https://github.com/nodejs/node/pull/11829


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>