repl: make own properties shadow prototype properties

Previously, the code displayed properties backwards (e.g., showing
prototype properties before own properties).  It also did uniqueness
checks during this processing, so these checks were done backwards.

After this change, the properties continue to be displayed backwards,
but the uniqueness checks are done in the proper order.

See also: https://github.com/nodejs/node/issues/21586 which was
discovered during the testing of this fix.

Fixes: https://github.com/nodejs/node/issues/15199
PR-URL: https://github.com/nodejs/node/pull/21588


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>