Implement the TestUtils namespace from
https://testutils.spec.whatwg.org/.
This should make the `js/builtins/weakrefs` tests run faster and more
consistently.
This change will enable other WPT tests but no tests exist currently for
TestUtils itself.
Fixes: #36290
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Signed-off-by: Sebastian C <sebsebmc@gmail.com>
Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
Co-authored-by: sagudev <16504129+sagudev@users.noreply.github.com>
