(Bug 58001) Handle trailing extlink-like text in a wikilink

* Added specialized productions to accept extlink text in wikilink
  content.

* Tweaked wikilink escape handler to not add nowikis around trailing
  "[..]" like text since the parser can now handle this correctly.

* Added a new parser test
  - fails html2wt and html2html mode since PHP parser output is not
    serializable into original wikitext

Change-Id: Ic641d4d5c82277fc04eaf73f72f3e8d6522b8326
Merge "(Bug 58001) Handle trailing extlink-like text in a wikilink"