Stdlib: withhold gd advertisement without host php-gd (#22740)

[PurHur]

Summary

• Gate GdExtensionPolicy::advertisesExtension() on host Zend extension_loaded('gd') so Docker images without php-gd no longer phantom-register gd_info / imagecreate / GdImage (re-Stdlib: extension_loaded('gd') true — imagecreate() stub without ext/gd (ext/gd/gd.c) #11675; undoes Stdlib: imagecreatefromstring() — GD decode from binary string (ext/gd/gd.c) #6215 always-true).
• Skip functional gd_* / image* compliance when withheld; keep extension_loaded_gd_phantom.phpt as the Zend-parity guard.
• PHP-in-PHP decode/draw stays in-tree for hosts that actually load php-gd.

Closes #22740

php-src reference

• ext/gd/gd.c — module init gates image* / gd_info
• ext/standard/info.c — extension_loaded / module registry

PHP implementation

• ext/gd/GdExtensionPolicy.php — host-extension advertisement gate (+ compliance helpers)
• ext/gd/Module.php — still under standard; getAdditionalExtensionNames() driven by policy

Test plan

• Docker (Zend gd=0):

./script/docker-exec.sh -- bash -lc 'export PHP_COMPILER_HELPER_RUNTIME_O=1
php test/repro/gd_extension_loaded_phantom.php
php bin/vm.php test/repro/gd_extension_loaded_phantom.php
php bin/compile.php -o /tmp/gd_phantom_aot test/repro/gd_extension_loaded_phantom.php
/tmp/gd_phantom_aot
php vendor/bin/phpunit --filter "GdExtensionPolicyTest|GdModuleSkeletonTest|extension_loaded_gd_phantom|ImagecreatefromstringTest"'

Zend/VM/AOT all:

loaded=no
gd_info=no
imagecreate=no
in_list=no
funcs=no

PHPUnit: OK (6 tests, 1 skip when host lacks gd)

Gate probe (this run)

Gate	Status
inventory (release-readiness)	ok
release-readiness	red — first fail north-star5-fast / 4f-m gen-0 manifest (#22642; not this PR)
issue repro VM+AOT	green

Made with Cursor