Add Async#evalOn(executor) or Async#evalOnExecutor(executor)

[armanbilge]

Async#evalOn takes a Scala ExecutionContext but frequently this functionality is needed for running on a Java Executor.

• ExecutionContext.fromExecutor(...) can be used to get an ExecutionContext from an Executor

• We can do even better, by using the current ExecutionContexts reportFailure method for the new ExecutionContext built from the Executor. This is better than the default reporter.

[homycdev]

Just to understand more clearly. You would like to add def evalOn[F](ec: ExecutionContext) = ??? inside object Async?

Or you want to change the initialization of the blockingExectionContext so when it fails, it would generate a report through reportFailure ?

[armanbilge]

You would like to add def evalOn[F](ec: ExecutionContext) = ??? inside object Async?

We already have this one :)

cats-effect/kernel/shared/src/main/scala/cats/effect/kernel/Async.scala

Lines 161 to 167 in 7e24bb9

	/**
	* Shift execution of the effect `fa` to the execution context `ec`. Execution is shifted back
	* to the previous execution context when `fa` completes.
	*
	* evalOn(executionContext, ec) <-> pure(ec)
	*/
	def evalOn[A](fa: F[A], ec: ExecutionContext): F[A]

I propose we add:

def evalOn[A](fa: F[A], exec: java.util.concurrent.Executor): F[A] 

[homycdev]

@armanbilge could you please review the PR attached to the issue, if possible? If you could not, I'd be glad if you'd tell me who could review the PR. Thanks!