Cancel children from activity coroutines instead of job itself

[AllanWang]

https://proandroiddev.com/kotlin-coroutines-patterns-anti-patterns-f9d12984c68e

Perhaps add base fragment? Coroutines also has MainScope now so I'm not sure if we should delegate to that too

[AllanWang]

We're not reusing jobs so it seems better to cancel the job itself. Otherwise users can still submit jobs when an activity is destroyed