Fix property hook asymmetric set visibility (#6898)

[PurHur]

Summary

• Parse PHP 8.4 set (protected|private|public) => / block hook syntax in PropertyHooks and emit phpc-asymmetric-set markers on the lowered property declaration.
• Enforce asymmetric set visibility before set-hook dispatch in the VM so global-scope writes throw Zend-parity Error instead of silently invoking the set hook.
• Add compliance PHPT + unit tests.

php-src reference

• Zend/zend_compile.c — asymmetric set modifier on property hooks
• Zend/zend_property_hooks.c — hook dispatch with visibility

PHP implementation

• lib/SourcePreprocessor/PropertyHooks.php — parse + lower asymmetric set hooks
• lib/VM.php — enforceAsymmetricPropertyWrite() before dispatchPropertySetHookAssign()

Verification

Issue repro (VM):

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php -r "class C{public string \$x{get=>\"g\"; set(protected)=>\$value;}} \$c=new C; echo \$c->x,\"\n\"; try{\$c->x=\"n\";}catch(Error \$e){echo get_class(\$e),\": \",\$e->getMessage(),\"\n\";} echo \$c->x,\"\n\";"'

Output:

g
Error: Cannot modify protected(set) property C::$x from global scope
g

Targeted tests:

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter "PropertyHooksTest::testLowersAsymmetric|property_hook_asymmetric"'

Result: OK (3 tests, 9 assertions)

Closes #6898

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