Add compute combinators

[BalmungSan]

Related to #3353

Adds a couple of useful combinators related to compute-bound operations.
How best to suspend compute-bound operations is a FAQ in Discord, thus I believe having some combinators for the simple use cases is a good idea.

[satorg]

I would like to weigh in a little.
I'm not sure that adding these two methods: computeAttempt and computeMapAttempt is really worth it:

def expensiveComputation: Either[Throwable, TheResult] = ???

computeAttempt { expensiveComputation } <=?=> compute { expensiveComputation }.rethrow

Thereby, computeAttempt doesn't look like a big win.

Is it really important to have rethrow executed before the finalizing cede rather than after it?

[satorg]

That said, compute and computeMap look like a big deal to me...

[BalmungSan]

I'm not sure that adding these two methods: computeAttempt and computeMapAttempt is really worth it:

As with any combinator is hard to argue both ways IMHO.
They are there for convenience, but I do agree it is impractical to add each and every combinator, as Fabio points regularly.
Like, compute is also just convenience, but I do agree the name would help and it seems folks are reluctant of using cede.

Personally, I like avoiding the rethrow but I also understand that it may not be seen as much, so I am happy to remove them if others agree.