Fix #70359 and #78577: segfaults with DOMNameSpaceNode

* Fix type confusion and parent reference
* Manually manage the lifetime of the parent
* Add regression tests
* Break out t

Fix #70359 and #78577: segfaults with DOMNameSpaceNode

* Fix type confusion and parent reference
* Manually manage the lifetime of the parent
* Add regression tests
* Break out to a helper, and apply the use-after-free fix to xpath

Closes GH-11402.

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Add missing EXTENSION section to tests

Fix return type of DOMNodeList::item()

It can also return DOMNameSpaceNode :(