Updates to handling of templated attributes

* This patch updates parser output for templated attributes to
  conform to the new spec @
  https://www.mediawiki.org/wiki/Parsoid/MediaWiki_DOM_spec#Transclusion-affected_attributes

* The serializer has been fixed up accordingly as well. But,
  the serializer continues to support the old spec for backwards
  compatibility till the time we purge the parser cache and get
  rid of old HTML completely.

* There are currently 2 failing wt2wt tests that correspond to
  entire "k=v" string being processed via *include* directives.
  There is a hack in attribute-expander that could be expanded
  to support them, but unclear if we have to continue supporting
  them and they are valid use cases. The selser failures are
  likely either a result of selser being more accurate than wt2wt
  but being tagged failing because of mismatch with wt2wt output.

* The other 10 failing selser tests correspond to these two tests:

2. includeonly in html attr value
Sanitizer: Validating that <meta> and <link> work, but only for Microdata

  These are cases where selser is more accurate than wt2wt. With
  change in parse output, for both these tests, there has been
  a reshuffling of failing and passing selser tests without any
  net change.

* Now, 20 additional wt2html tests are passing because of the
  absence of meta-tags from the earlier spec and all templated
  attr info being recorded in data-mw. data-mw is stripped out
  while comparing HTML output with PHP output and all these tests
  now pass.

Change-Id: I4d132e611547996e99b8376e089bc6fa5b9b63bf