WTS: Improved consistency + bug fixes handling whitespace in text nodes.

* Now, all leading whitespace is stripped from a text node and
  made part of separator text before it since separator handling
  has a lot more intelligence dealing with indent-pres and the
  nowiki-escaping algorithm doesn't.

  Ex: <ul><li>\n foo</li></ul>

  Here, the leading whitespace on a newline in "\n foo" does not
  lead to indent-pres and doesn't need nowiki escaping because
  <li> is a strong indent-pre suppressing node.

* ZeroWikitextWidthNode information was not checking if the node
  is a literal HTML node. Fixe this by adding a helper method in
  DOMUtils and using the helper.

* Fixed a bug in DU.precedingSpaceSuppressesIndentPre to skip over
  the node that contributed separator text.

* <P> is also a strong-indent-pre suppressing tag. Check this in a
  sandbox: "<p>\n  foo\n<p>\n\n<p>\n  <span>\n   bar\n</span>\n</p>"

* Given the A-B node pair, makeSepIndentPre was mixing up notions of
  indent-pre suppression (induced by nodeA and which affects nowiki
  wrapping) and sensitivity to space chars in sol-position (applies
  to nodeB and requires whitespace stripping). This patch separates
  those notions and fixes things up.

* After all these bug fixes:
  - one blacklisted selser test now green.
    (because non-selser output improved and matched selser).
  - output of previously blacklisted tests changed.
    The change makes sense. The first nowiki is to suppress indent-pre
    on the first line. The second nowiki is to suppres indent-pre and
    <td> rendering for the | char on the second line.

Change-Id: Id6edbc0b0804995c02ce61a9e1ba52d63af58e91
Merge "WTS: Improved consistency + bug fixes handling whitespace in text nodes."