repl: handle stage-3 language features properly

This adds stage-3 language features to acorn so that the REPL is
able to parse these features properly. Otherwise these would cause
SyntaxErrors.

PR-URL: https://github.com/nodejs/node/pull/27400
Fixes: https://github.com/nodejs/node/issues/27391
Fixes: https://github.com/nodejs/node/issues/25835


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>