I tried to avoid unrelated refactorings. The only thing I ended doing
is turning a huge if-else around into a guard-clause.
Main motivation here is:
* Make the huge, almost 2000 line Cite class smaller.
* Turn public code into private implementation details.
Bug: T236260
Change-Id: Ifca28040ae60d021a31aaee65417c7584627a975
* I used https://codesearch.wmflabs.org to make sure the private
constants are indeed not used anywhere.
* The added type hints are safe, as far as I can tell. There is no way
one of these parameters can contain anything else. Otherwise the code
would fail already.
Change-Id: Iaa7615e9864805760fa652700b58b69680b4f17e
