Fix GH-23116 and GH-23117: stack overflow when normalizing a deeply nested document

[lazerg]

DOMNode::normalize() and Dom\Node::normalize() walk the tree by recursing once per element child, so a deeply nested document exhausts the C stack and segfaults. Both now check the stack limit on entry and throw an Error, the same way the XML serializer has since GH-22570.

The throw is gated on EG(exception) because these functions return void: without it, unwinding through a tree that is wide at the overflow depth throws once per node and chains the Errors, which is quadratic.

Fixes #23116
Fixes #23117

[devnexen]

nit: can we exercise this test somewhere ?

$doc = new DOMDocument();
$root = $doc->createElement('root');
for ($s = 0; $s < 2; $s++) {
    $node = $doc->createElement('a');
    for ($i = 0; $i < 100000; $i++) {
        $parent = $doc->createElement('a');
        $parent->appendChild($node);
        $node = $parent;
    }
    $root->appendChild($node);
}
$doc->appendChild($root);

try {
    $doc->normalize();
} catch (\Error $e) {
    echo "wide: ", $e::class, ": ", $e->getMessage(), "\n";
    **var_dump($e->getPrevious());**
}

expecting

wide: Error: Maximum call stack size reached. Infinite recursion?
NULL

[lazerg]

Added. Both tests now build two deep branches under one root and assert that getPrevious() is NULL. I checked that this assertion does fail if I drop the !EG(exception) gate, so it exercises the case you meant.

I also moved the tests off loadXML() while I was in there. The FreeBSD job capped the parse depth at 2048 even with LIBXML_PARSEHUGE, so the tree never got deep enough to reach the guard. Building through the DOM API at depth 25000 with a 256K stack limit gives the same coverage and runs in about 2.5s.

[LamentXU123]

Thanks!