Fix GH-20503: Assertion failure with ext/date DateInterval property hash construction

[heathdutton]

A DateInterval that references itself trips an assertion in json_encode() on debug builds. date_object_get_properties_interval writes into the properties table in place. While json_encode() walks the cycle, that table is shared (refcount > 1), so zend_hash_str_update() asserts.

Now the handler separates the table first and writes the copy back to obj->properties, so it doesn't leak.

A direct self-reference ends in "Maximum stack depth exceeded" now, same as DateTime. A cycle through an array still reports "Recursion detected".

Fixes GH-20503

[arnaud-lb]

Thank you @heathdutton! The approach looks right, but please check comments. (Edit: Please change the base of the PR to PHP-8.3. The branch is based on 8.3, but not the PR.)

[arnaud-lb]

NB: In master, DateInterval could be greatly simplified by using standard object properties and removing all the prop handlers.

[heathdutton]

I tried adding the refcount check to get_properties_interval, but it leaks memory - the duplicated HashTable has no owner to free it. Other routes I tried produced ABI break, so I reverted a bit to get us passed the block. The ABI break label no longer applies.

[heathdutton]

Reworked per your suggestion. get_properties_interval now separates the table when it's shared and writes the dup back to obj->properties (that was the leak I hit before). The get_properties_for handler is gone, and the test uses the json_encode() repro, which aborts without the fix.

A direct self-reference now ends in "Maximum stack depth exceeded", same as DateTime. Moved the base to PHP-8.4 since 8.3 is security-only now. Mind another look when you get a chance?

[arnaud-lb]

Looks good to me otherwise

[arnaud-lb]

Thank you!