Fix bug in dl-dt list output generation

Fix bug in dl-dt list output generation

* An open <dt> (;) should be closed when we encounter a new <dd> (:)
  char even if it is on a new line that has other nested lists inside.

* Tidy was hiding this PHP parser bug by closing a <dt> and opening
  a <dd> when given this HTML: "<dl><dt>a<ul><li>b</li></ul></dt></dl>"
  It generates "<dl><dt>a</dt><dd><ul><li>b</li></ul></dd></dl>"

  However, a HTML5 parser like RemexHTML, domino (used by Parsoid),
  or browsers don't do this fixup.

* So, what I thought was a bug in RemexHTML turned out to be a bug
  in the PHP parser that was being hidden by the use of Tidy.

* Added a regression test.

Bug: T175099
Change-Id: I6d5b225b82cecf9a43f23837ed8ec359b31aadad