feat: Add way to abort obsolete async computed promises

[Nokel81]

Motivation:

• AbortSignal is the standard way to pipe "cancellation" through async calls

[jansav]

What's the use case for this? Description doesn't describe it enough so that I could understand.

Unit tests are written in very technical manner and therefore understanding the use case is hard. Lets describe the use case in unit tests to figure out the solution.

Is the motivation to abort promise when asyncComputed is unobserved? If so, the implementation doesn't do it.
However, that could be something that asyncComputed would do.

It would be preferrable that the change to TS would be in separate commit to make reviewing easier.