Fix Scala-js fetch manual abort v4

[ThijsBroersen]

This PR implements cancellation of fetch-request when effects are interrupted.
I tested it manually with a local project. I was unsure on how to adjust/add a unit test to validate the behaviour.

Before submitting pull request:

• Check if the project compiles by running sbt compile
• Verify docs compilation by running sbt compileDocs
• Check if tests pass by running sbt test --> could not run the tests because I don't have the required browser
• Format code by running sbt scalafmt

[adamw]

Thanks :)