vm: use SetterCallback to set func declarations

Currently, when in strict mode, function
declarations are copied on the sandbox by
CopyProperties(), which is not necessary
and will break when CP is removed.

This change maintains current behavior,
letting GlobalPropertySetterCallback
copy functions on the sandbox instead
of using CP to do the task.

PR-URL: https://github.com/nodejs/node/pull/12051


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>