* Replace lodash 'values' usage with Object.keys => .map(obj[key])
* Block scoping: refactor letReferences, outsideLetReferences as objects of type Map
* Remove lodash dependency from babel-plugin-transform-block-scoping
* Fixup: Add missing Object.keys call
* Fixup: Update remaining property accessors
* Coerce Map.values() iterator results into an array via spread operator
* Fixup: Map.put -> Map.set
* Fixup: undo incorrect variable de-duplication
* Replace array-spread-plus-map combination with Array.from call
* Extract an extendMap function as an attempt to create an optimization boundary
* Experiment: cast objects to string (eliminates one Map/object difference per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map )
* Fixup: perform String cast on map keys, not values
* Revert "Fixup: perform String cast on map keys, not values"
This reverts commit abdd147438fa74f51ac50ef1f96bb462810cd3f2.
* Revert "Experiment: cast objects to string (eliminates one Map/object difference per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map )"
This reverts commit a4035c885b37bfd6e926a0362bda9dcf5b5a52c2.
* Experiment: filter keys via Object.prototype.hasOwnProperty.call
* Revert "Experiment: filter keys via Object.prototype.hasOwnProperty.call"
This reverts commit 491c093f213c6229815b2e6dc9243245376265b0.
* Migrate back from Map-based reference storage to Object-based storage; access performance appears much improved for Object property access
* Revert "Migrate back from Map-based reference storage to Object-based storage; access performance appears much improved for Object property access"
This reverts commit 2119acc7f0d78ced3b9ad77820b4b72e5ad67475.
* Iterate over a clone of outsideRefs keys
* Revert "Extract an extendMap function as an attempt to create an optimization boundary"
This reverts commit 85689f2bfc180d0b5c0e674e5de7954470c7ec69.
* Fixup: migrate remaining Object property access to Map.get in tdz module
