fix(symfony): isolate api_platform.property_info tags

[soyuka]

Summary

api_platform.property_info extractors were tagged with the global Symfony property_info.* tag namespace in #7969. Symfony's framework property_info service consumes tagged_iterator('property_info.type_extractor') and so picked up API Platform's PhpStanExtractor too — including in the chain used by validator.property_info_loader.

On projects depending on doctrine/persistence / doctrine/common (e.g. Sylius), bin/console cache:clear then crashes inside the validator while walking Doctrine interfaces carrying @template T of object:

Symfony\Component\TypeInfo\Exception\InvalidArgumentException
  Cannot create union with both "object" and class type.
  at UnionType.php:75
  Symfony\Component\TypeInfo\Type::union()
  Symfony\Component\TypeInfo\TypeResolver\StringTypeResolver->getTypeFromNode()
  Symfony\Component\PropertyInfo\Extractor\PhpStanExtractor->getType()
  ApiPlatform\Symfony\Validator\Metadata\Property\ValidatorPropertyMetadataFactory->create()

This PR renames the tags to api_platform.property_info.* (private namespace) and updates the PropertyInfoExtractor composing service to consume the private tags. The framework's property_info is no longer mutated by API Platform, restoring the design intent expressed during #7969 review ("stop touching framework.property_info entirely").

• src/Symfony/Bundle/Resources/config/api.php — three extractors (reflection / php_doc / phpstan) and the composing PropertyInfoExtractor switch from property_info.* to api_platform.property_info.*.
• Added testPropertyInfoExtractorsDoNotLeakIntoFrameworkPropertyInfo regression test asserting tag isolation.

Test plan

• vendor/bin/phpunit --filter testPropertyInfoExtractorsDoNotLeakIntoFrameworkPropertyInfo — passes (15 assertions)
• vendor/bin/phpunit tests/Symfony/Bundle/ApiPlatformBundleTest.php — passes
• rm -rf tests/Fixtures/app/var/cache/test && tests/Fixtures/app/console cache:clear --env=test — clears cleanly
• CI green
• Reproducer on a Sylius-based project (via composer link of this branch) — confirmed cache:clear exits 0

Fixes #8201
Refs #7969