[model] refactor model document tests to use a shared testing function
Created attachment 451871 [details] Patch
Committed r289733 (247218@main): <https://commits.webkit.org/247218@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 451871 [details].
<rdar://problem/88900706>
rebased http/tests/model/model-document.html in https://trac.webkit.org/changeset/289898/webkit