tearDown order needs to be upstream->downstream on consumer-initiated unsubscription

About

• wpt test "Teardowns are called in upstream->downstream order on consumer-initiated unsubscription" fails

Expected behavior

• tearDown order:
  • "upstream abort handler"
  • "upstream teardown. reason: Abort!"
  • "middle abort handler"
  • "middle teardown. reason: Abort!"
  • "downstream abort handler"
  • "downstream teardown. reason: Abort!"

Current behavior

• tearDown order:
  • "downstream abort handler"
  • "middle abort handler"
  • "upstream abort handler"
  • "upstream teardown. reason: Abort!"
  • "middle teardown. reason: Abort!"
  • "downstream teardown. reason: Abort!"

How to reproduce

• npm run test-serve and inspect wpt test results in the browser

Additional context

https://github.com/keithamus/observable-polyfill/blob/5af5df1b6bb87abc44a773701ebcf64c1d1f25c7/test/wpt/observable-constructor.any.js#L728-L763