WTS: Post-processing to remove unnecessary indent-pre nowikis

* WTS doesn't have enough context to suppress unnecessary indent-pre
  nowikis. Ex: lines that have a block tag on it.

* This patch adds a post-processing pass that strips such nowikis
  where it can safely determine that indent-pre nowikis will
  get suppressed.

* The pass is only run if indent-pre nowikis have been added in the
  first place. So, this doesn't affect the common case where nowikis
  aren't added.

* Eliminates an unnecessary <nowiki> in a blacklisted selser test
  and improves its accuracy.

Change-Id: I6da350ac76c208cb07b26b8ecbfe80654691a512
Merge "WTS: Post-processing to remove unnecessary indent-pre nowikis"