Leading ws before figure wikitext doesn't need nowikis

* FIGURE was missing in the list of leading-ws-accepting-tags
  in wikitext.constants.js

* Added a new parser test.

* Fixes a rt-diff on
  enwiki:Ch%C3%A2teau_de_Saint-Germain-en-Laye?oldid=613333885

* Made minor cleanups to a comment.
* Fixed a test for indent-pre safety since the test doesn't really
  care about presence/absence of sepType anymore.

Change-Id: Ife1bc5a3061dca32ce08de88412ac6ae4283a9be
Merge "Leading ws before figure wikitext doesn't need nowikis"