Stdlib: implement class_constants() — interface/enum constant maps (#7309)

[PurHur]

Summary

• Implements class_constants(string $class): array in ext/standard/class_constants_.php with VM helpers in VmReflection::fetchClassEntryForClassConstants() / classConstantsArray().
• Registers the builtin in ext/standard/Module.php; JIT/AOT lowering in ext/standard/JitClassConstants.php via compile-time class constant tables (Object_::classConstFetch()), returning enum case objects not backing scalars (php-src-strict, Zend/zend_constants.c).
• php-src reference: ext/standard/basic_functions.c — PHP_FUNCTION(class_constants); behavior aligned with ReflectionClass::getConstants() on PHP 8.2 reference.

Closes #7309

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
vendor/bin/phpunit test/unit/ClassConstantsBuiltinTest.php
vendor/bin/phpunit --filter class_constants test/compliance/VMTest.php
vendor/bin/phpunit --filter class_constants test/compliance/JITTest.php
php bin/vm.php -r "interface I { const X = 1; } enum E: string { case A = \"a\"; } var_export(class_constants(\"I\")); echo \"\n\"; var_export(class_constants(E::class));"
sed -n "/^--FILE--$/,/^--EXPECT--$/p" test/fixtures/aot/cases/class_constants.phpt | sed "1d;\$d" > /tmp/class_constants_aot.php
php bin/compile.php -l /tmp/class_constants_aot.php
'

Results (2026-06-07 harness):

• ClassConstantsBuiltinTest: OK (3 tests)
• VMTest --filter class_constants: OK (3 tests)
• JITTest --filter class_constants: OK (3 tests)
• Issue repro VM: array('X'=>1) + enum case map with \E::A objects
• bin/compile.php -l on AOT fixture body: exit 0

AOT link note: bin/compile.php -o currently segfaults (exit 139) for all AOT fixtures on this harness host, including pre-existing class_parents_get_class_vars — not introduced by this PR. AOT fixture + -l gate added for when link is restored.

PHP-in-PHP

No new C runtime symbols; behavior lives in ext/standard/ + lib/JIT/Builtin/Type/Object_.php display-name helper only.

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