[php-src] PR #25110: Fix GH-25108: Skip uninitialized hooked properties in json_encode()

Pull Request: https://github.com/php/php-src/pull/25110 Author: JoaoMarcos44 Fixes #25108. > AI-assisted contribution. The patch, regression test, and explanation were prepared with AI > assistance and checked with local builds and tests. ## Summary > Omit an uninitialized backed property when reading it through a setter hook during JSON > encoding. Previously, adding a setter hook changed an omitted field into an explicit null. > The encoder skips the uninitialized sentinel before emitting a property name. Explicit null > values and getters returning null remain included. The PHPT also checks initialized values, virtual > set-only properties, ordering, and pretty printing. A NEWS entry records the fix. ## Validation > Target: PHP-8.4, the lowest actively supported affected branch. > Built with --enable-debug --enable-zts. > - The new regression fails before the fix and passes afterward. > - make -j1 passes. > - make -j1 test TESTS="ext/json/tests > Zend/tests/property_hooks" passes with 291 passed and 5 skipped. No failures or > warnings. The skips concern unavailable zend_test support and locales. The test runner uses one > worker. > - The full PHP suite and Windows builds were not run. <details> <summary>Illustrated explanation</summary> > AI-generated conceptual illustration. The issue contains the executable reproduction.  [Explanation and prompt](https://github.com/JoaoMarcos44/php-src/blob/9e60fedb55c1c3bdfaeb339f1beeae2895526596/assets/json/infographic_report.md) </details>