`FlatMap.map2Eval` is not lazy and blows the stack in cases where it probably shouldn't

[satorg]

The current implementation of the FlatMap.map2Eval is the following:

cats/core/src/main/scala/cats/FlatMap.scala

Lines 116 to 117 in 8681c88

	override def map2Eval[A, B, Z](fa: F[A], fb: Eval[F[B]])(f: (A, B) => Z): Eval[F[Z]] =
	Eval.now(flatMap(fa)(a => map(fb.value)(b => f(a, b))))

If that implementation is used inside Foldable.foldRight it blows the stack very easily:

val G = Applicative[OptionT[Id, *]]

Foldable[List]
  .foldRight(List.range(0, 12345), Eval.now(OptionT.pure[Id](0L))) { (a, accEvalG) =>
    G.pure(a).map2Eval(accEvalG) { _ + _ }
  }
  .value

Note: even though Applicative is summoned, since OptionT is a Monad, it implements FlatMap too. And since it doesn't override map2Eval, the one from FlatMap is used.