Fix DSR for misnested A-tags to prevent selser corruption

* Adding any content in the same paragraph as the misnested A-tag
  @ https://en.wikipedia.org/wiki/User:Ssastry/VE_Test#Nested_A-tag_tests
  will cause selser-based corruption of that fragment.

* This patch eliminates that corruption. Manually tested with the
  snippet locally.

* Since the fixup relies on wrapping bare text nodes with a <span>,
  I split off 2 tests into PHP-only and Parsoid-only tests with
  different HTML output.

  The <span> wrapping now causes additional selser failures since
  selser will avoid the wrappers but wt2wt will not be able to,
  and selser output will marked as the faulty output.

Change-Id: I30bc3bf6d8f4c54d02b12eb7686a4b1e58ed584a
Merge "Fix DSR for misnested A-tags to prevent selser corruption"