Fix various hooked object iterator issues

Fixes GH-16185
Closes GH-16281

Fix handling of undef property during foreach by ref on hooked class

Fix various hooked object iterator issues (GH-15394)

Fixes GH-15187

[RFC] Property hooks (#13455)

RFC: https://wiki.php.net/rfc/property-hooks

Co-authored-by: Nikita Popov <nikita.ppv@gmail.com>