mapSourcePosition() will try to load the compiled script’s text and
extract its source map. When the source map is found, the module will
cache it, but when the script just doesn’t have any source map at all,
the module doesn’t remember that, and will load the script text again at
every subsequent call.
If you have your own uncaughtException handler, you might still like the
pretty source display from handleUncaughtExceptions: true; therefore
expose it as exports.getErrorSource(err)
