* Track thisContainer for this-property-assignments in JS
Previously it would update on every block, not just those that could
bind `this`.
In addition, if the constructor symbol still can't be found, then no
binding happens. This is usually OK because people don't add new
properties in methods too often.
* Update additional baselines
* Add lib:dom to new test
* Address PR comments
* Correct new name for saveThisParentContainer
