Clean up Language::markNoConversion().

Clean up Language::markNoConversion().

* IRIs are getting more and more widely used these days so Chinese
  characters are also needed to be prevented from being converted
  in text of external links.
* So now all markNoConversion() functions in languages with variants
  do the same thing. Merge them into a single function in the
  Language class and drop implementations in individual languages.
* By the way rephrase phpdoc of that function, and (bug 24798) fix
  the link detection regex to use wfUrlProtocolsWithoutProtRel().
  Protocol-relative regex is excluded to avoid false positives.
* Add parser test for it.

Change-Id: I2ec0ac2b9b11221584adb72555168498de209d57