mediawiki.htmlform: Fix broken $() call

mediawiki.htmlform: Fix broken $() call

Follows-up c310e7b40c, daa92bb06e.

The $( Array ) signature requires the list to contain DOM nodes,
not jQuery objects. The fields variable should be a list of
nodes, not jQuery collections.

Also:
* Improve @return documentation for hideIfParse().
* Flag hideIfParse() and hideIfGetField() as private to remove them
  from the jQuery#htmlform API documentation as methods that would
  be mixed into the jQuery prototype (they're not).

Bug: 67685
Change-Id: I4bb93ad234cdd4a1f412b759065138e2831be2a6