mediawiki.jqueryMsg: Rename .parser class to .Parser

mediawiki.jqueryMsg: Rename .parser class to .Parser

This class is marked @private, but nonetheless, there is at least
one use in MobileFrontend, so keeping a back-compat alias for now.

Also rename the HtmlEmitter utility class (also private, not used
anywhere outside this file), and fix its broken documentation by
repeating the @class and @private tags on its own constructor.
It previously had all its methods indexed by JSDuck as part of the
previous class in that file (Parser), which created doc pages
with examples that don't work.

Change-Id: I02d851d9b6eac89f1a2b85b438b982bd055bedee