Fixed DSR errors introduced by DOM spec changes

* DSR computation used DOM Spec markers on A-tags to detect
  source wikitext syntax in computing dsr tag widths. This code
  went out ofsync with DOM spec changes.

* This patch introduces helpers to detect a-tag source syntax
  and adds additional data-parsoid markers for rfc/pmid/isbn
  uses.

* Eliminated lower-case html tag names in
  mediawiki.wikitext.constants.js which got rid of the only
  lower-case HTML tag names in that file.

* No change in parser test results but 25 fewer DSR warnings
  and eliminates NaN entries.

Change-Id: Idf0a15d64739da5d82f0632864987ff547daded6
Merge "Fixed DSR errors introduced by DOM spec changes"