I don't like that I had to special-case `<p>` tags (top-level
comments) in this code. I feel like it should be possible to handle
top-level comments and replies in a generic way, but I couldn't find
a way to do it that actually worked.
Notes about changes to the behavior, based on the test cases:
* Given a top-level comment A, if there was a "list gap" in the
replies to it: previously new replies would be incorrectly added at
the location of the gap; now they are added after the last reply.
(T242822)
Example: "pl", comment at "08:23, 29 wrz 2018 (CEST)"
* Given a top-level comment A and a reply to it B that skips an
indentation level: previously new replies to A would be added with
the same indentation level as B; now they are added with the
indentation level of A plus one. (The old behavior wasn't a bug, and
this is an accidental effect of other changes, but it seems okay.)
Example: "pl", comment at "03:22, 30 wrz 2018 (CEST)"
and reply at "09:43, 30 wrz 2018 (CEST)"
* Given a top-level comment A, a reply to it B, and a following
top-level comment C that starts at the same indentation level as B:
previously new replies to A would be incorrectly added in the middle
of the comment C, due to the DOM list structure; now they are added
before C. (T241391)
(It seems that comment C was supposed to be a multi-line reply that
was wrongly indented. Unfortunately we have no way to distinguish
this case from a top-level multi-line comment that just happens to
start with a bullet list.)
Example: "pl", comments at "03:36, 24 paź 2018 (CEST)",
"08:35, 24 paź 2018 (CEST)", "17:14, 24 paź 2018 (CEST)"
* In the "en" example, there are some other changes where funnily
nested tags result in slightly different results with the new code.
They don't look important.
* In rare cases, we must split an existing list to add a reply in the
right place. (Basically add `</ul>` before the reply and `<ul>`
after, but it's a bit awkward in DOM terms.)
Example: split-list.html, comment "aaa"; also split-list2.html
(which is the result of saving the previous reply), comment "aaa"
* The modifier can no longer generate DOM that is invalid HTML, fixing
a FIXME in modifier.test.js (or at least, it doesn't happen in these
test cases any more).
Bug: T241391
Bug: T242822
Change-Id: I2a70db01e9a8916c5636bc59ea8490166966d5ec
