(Bug 50218) Generated DOMFragment wrapping <ol> for references tag

* So far, references wikitext was being replaced with a meta marker
  token that participated as an inline token in p-wrapping.  As a
  result, in some cases, a p-tag was wrapping the references ol-node
  which is buggy HTML.  When VE loaded this DOM, the p-node was split
  around the ol-node and duplicated DSR which led to duplicated
  output when selser ran on this.

* One way of fixing this would have been to add a special case in
  the paragraph wrapper to treat the mw:Extensions/References/Marker
  meta tag as a block token.

* A better solution with an eye towards the longer-term is to emit
  mw:DOMFragment wrapper for the references tag with the content
  being an ol-node. The dom-fragment unpacking code then takes care
  of p-wrapping issues for the ol-node. This fixes the bug in this
  case.

* Also fixed parser tests output where group attribute was missing
  on some tests (which indicated that the older code was not emitting
  the group attribute on references tag).

* No change in parser tests.

Change-Id: I073b2e68667d577c75cad07d19cea2b19d0e89fe
Merge "(Bug 50218) Generated DOMFragment wrapping <ol> for references tag"