Previously they were added at the end of the text node containing the
timestamp, which was usually the end of the line, but not always.
And also fix the same problem for inserting the actual replies (or
reply widgets). This replaces an undocumented hack that prevented our
own reply links from triggering this bug (without it, the reply widget
would be inserted before the reply link rather than after).
While we're here, remove unintentional spacing that appeared before
some reply links, caused by trailing whitespace in text nodes.
Add tests for all of the above.
Bug: T245695
Change-Id: I354b63e2446bb996176a2e3d76abf944127f307e
