Implement several Functor methods to avoid using map when not needed

[johnynek]

I reached for tupleLeft in this PR:

typelevel/cats-collections#779

But then looked and noticed that actually it and related functions haven't been overridden in many places. This PR addresses that.

[johnynek]

I couldn't find the native error. I guess is may be some issue with the native being flakey? I can't see why the changes would fail on native but not JVM.

[danicheg]

Adding some tests would be nice. Anyway, LGTM

[johnynek]

Adding some tests would be nice. Anyway, LGTM

I've added some tests. Ideally these would be added to FunctorLaws saying that those methods need to match the map based implementations. Doing that, however, would break compatibility of FunctorLaws because it requires more Arbitrary and Eq instances (a major weakness of our Laws).

Honestly, I wonder if the laws need some higher kinded change. Something like ArbitraryK[[A] =>> [Arbitrary[A] => Arbitrary[F[A]]] and similiar for Eq and Cogen and then maybe define case class TestType[A](arbA: Arbitrary[A], eqA: Eq[A], cogenA: Cogen[A]) and then the system defines ArbitraryK[TestType] and then we could define new laws without requiring changes to the function types and breaking compatibility. But obviously this is a major rewrite of how the laws work.

[johnynek]

@danicheg how does this look? I think it is ready to merge.