Round-trip original image size string

This fixes some of the issues introduced in
https://gerrit.wikimedia.org/r/#/c/103082/14

* Fixed a bug in the way addNormalizedAttribute was called

* Round-trip the original size spec if the dimensions were not touched

* Serialize to 100x100px for a square bounding box, as just 100px is actually
  only limiting the width

* Update some of the image tests to actually reflect current parsoid output

* Remove unnecessary cacheKey entry from data-parsoid (bug 60006)

This patch will work out of the box on current HTML, as it uses the existing
option list for size spec round-tripping.

Bug: 60006

Change-Id: Ia2e6ff2ef3900871edfd884aa5a51c5f5c327666
Merge "Round-trip original image size string"