For example, in the following abbreviated test HTML:
<span>some text</span>
<script>println("whf")</script>
We would have to craft the expectation file to include the "some text"
segment, usually with some leading whitespace. This is a bit annoying,
and makes it difficult to manually craft expectation files.
So instead of comparing the expectation against the entire DOM inner
text, we now send the inner text of just the <pre> element containing
the test output when we invoke `internals.signalTextTestIsDone`.
In particular, get the implicit root correctly for intersection
observers that don't have an explicit root specified.
This makes it possible to load the Terminal app on https://puter.com/
It's perfectly possible for JavaScript to call unobserve() on an element
that hasn't been observed. Let's stop asserting if that happens. :^)
Fixes#22020
