(Bug 50420) Tweaked selser to reuse td/th/tr wrappers from source

* When only tr/td/th contents are modified, but the wrapper itself is
  unchanged, so far, the wrapper was being serialized from HTML rather
  than use selser to emit from source. The existing code conservatively
  assumed that the presence of autoInsertedEnd flags on nodes implied
  that the DSR on those nodes was untrustworthy. However, we can
  safely trust DSR on tr/td/th wrappers even in the presence of
  autoInsertedEnd flag being present.

* This immediately eliminates the problem of emitting an explicit
  <td> (pipe in wikitext) where original source used an implicit
  <td>.

* Tested with the following wikitext by editing 'foo' to 'fool'
  and serializing edited HTML.
{|
|-
foo
|}


* Note: The bug is not entirely fixed.  There is an unrelated
  parser bug that doesn't parse the leading "*a" in a td-cell as
  a list item.  That can be addressed in a different commit.

* 1 selser failure. This is because of the same reasons as
  documented in b4f62292. The selser test output is actually
  the correct output in this example.  Updated blacklist for now.

Change-Id: Ide10803a99d4034a4008bb2469011830011e434b
Merge "(Bug 50420) Tweaked selser to reuse td/th/tr wrappers from source"