Add `max_object_properties` parameter for `json_decode()`

Description

Currently, json_decode() is vulnerable to HashTable supercolliding, when integers are used as property names in assoc mode, or perhaps when strings with some known hashes are used. This can be trivially exploited to cause major performance issues in applications which accept JSON payloads from a client.

While this is obviously a tough issue to solve globally, I think allowing users of json_decode() to limit the max number of object properties would mostly eliminate the problem for JSON handling, since most use cases should know or be able to predict what the max reasonable size of an object should be. I think this should probably be fairly easy to implement.

A precedent for this does exist: max_input_vars was implemented to mitigate HashDoS for query parameters over a decade ago, so I don't think this is a crazy idea.

Disclaimer: I did already report a security issue for this and was told to create a feature request, so here it is.

Commencez au point d’entrée json_decode() et examinez le précédent de max_input_vars mentionné dans l’issue. Définissez comment un paramètre max_object_properties doit limiter les objets décodés, y compris son interaction avec le mode assoc, puis ajoutez une couverture montrant que les objets trop volumineux sont rejetés ou limités comme prévu.