Allow readonly properties with hooks (PHP 8.4) — Closes #9835

[PurHur]

Summary

• Remove compile-time Hooked properties cannot be readonly rejection in PropertyHooks preprocessor — PHP 8.4 allows readonly properties with set hooks initialized from the constructor.
• Existing VM readonly enforcement already handles runtime: constructor init via set hook succeeds; post-construct external writes throw catchable Error.
• Update compliance guards and unit test to match php-src-strict behavior (supersedes stale Language: property hook + same-name backing field — must parse-error (Zend/zend_compile.c) #9805 compile-fatal expectation).

php-src reference

• Zend/zend_compile.c — readonly + hook validation (PHP 8.4)
• Zend/zend_property_hooks.c — set hook during construction vs post-init write Error

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php test/repro/maintainer_gap_readonly_hook_write_exception.php'
# caught: Error

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./vendor/bin/phpunit --filter "readonly_property_hook|property_hook_readonly|testReadonlyHookedPropertyLowers"'
# OK (3 tests, 5 assertions)

Closes #9835

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