Add missing EXTENSIONS section to DOM tests

Fix GH-11288 and GH-11289 and GH-11290 and GH-9142: DOMExceptions and segfaults with replaceWith

This replaces the implementation of before and after with one following
the spec very str

Fix GH-11288 and GH-11289 and GH-11290 and GH-9142: DOMExceptions and segfaults with replaceWith

This replaces the implementation of before and after with one following
the spec very strictly, instead of trying to figure out the state we're
in by looking at the pointers. Also relaxes the condition on text node
copying to prevent working on a stale node pointer.

Closes GH-11299.

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