[PurHur]

Summary

• Register DOMNode::contains(?DOMNode $other): bool on the DOM node class hierarchy.
• Implement parent-chain walk in VmDom::contains() using DomRegistry state (php-src ext/dom/node.c).

Closes #14447

php-src reference

• ext/dom/node.c — dom_node_contains()
• ext/dom/node.stub.php — DOMNode::contains

Verification

./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/maintainer_gap_dom_node_contains.php'
# ok, exit 0

./script/docker-exec.sh -- bash -lc './vendor/bin/phpunit --filter DomModuleTest::test_dom_node_contains_descendant_check'
# OK (1 test)

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