Add PHP Core Roundup 18 (#120)

* Add PHP Core Roundup 18

* RFC1867 a little more detail

* Apply suggestions from code review

Co-authored-by: Ayesh Karunaratne <[email protected]>

* Update source/_posts/2023-11-01-php-core-roundup-18.md

* Update source/_posts/2023-11-01-php-core-roundup-18.md

Co-authored-by: Máté Kocsis <[email protected]>

* Update source/_posts/2023-11-01-php-core-roundup-18.md

Co-authored-by: Ayesh Karunaratne <[email protected]>

* Merge David CARLIER

* Update source/_posts/2023-11-01-php-core-roundup-18.md

Co-authored-by: Gina Peter Banyard <[email protected]>

* Minot text changes

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Co-authored-by: Ayesh Karunaratne <[email protected]>
Co-authored-by: Máté Kocsis <[email protected]>
Co-authored-by: Gina Peter Banyard <[email protected]>
Co-authored-by: Roman Pronskiy <[email protected]>