New parser tests for lang/category/wiki links (wt2wt and html2wt modes)

* Added new tests to catch regressions and document serialization
  behavior for new links from clients.

* We have one newly failing test because of bug 70960.

* We also have a newly failing selser test:
    "Interlanguage link variations [3,2,2,0,1,2,1,3,0]"
  This seems to be a selser bug where it isn't able to track the
  deleted newline between the two link tags (or it seems to be
  carrying over a newline separator from the previous nodes).
  This is not a serious bug. Separator handling is tricky in
  general, and this is one of those failing scenarios.

Bug: 70894
Bug: 70960
Change-Id: I92deb78fb8f4d7746bfe6d657e50a875c3675ab6
Merge "New parser tests for lang/category/wiki links (wt2wt and html2wt modes)"