* refactor: simply browserslists defaults overwriting
When `hasTargets` is `false`, `targets` is always an empty object by definition, `objectToBrowserslist({})` always return `[]` therefore we can remove `objectToBrowserslist`.
* test: apply external-helpers on preset-env test fixtures
* test: add ie 6 to force all transforms in corejs 3, debug, corejs 2 fixtures
* Add ie 6 as targets for test fixtures
* Revert "Move subclass inheritance to end (#7772)"
This reverts commit f8ab9466d331871a90f458af40b14e8d831e0c29.
* Only use getPrototypeOf if setPrototypeOf is implemented
* Update fixtures
* Helpers updates
* Update fixtures
* Fall back to getPrototypeOf
* Update fixtures
We were using `Object.create` to setup the prototype chain at the start of the class definition, which lead to #7771.
I was a bit worried about a speed hit, but it seems everyone optimizes the two patterns the same way.
https://jsbench.github.io/#f9fca52407643d96458a35763b201215Fixes#7771.
