Add method forwarders to `Resource`

Resource implements Async, but does so in a purely “typeclassy” way. If you want to do something like rsrc.start (where rsrc: Resource[F, A]), you actually need to import cats.effect.syntax.all._! This isn’t a great experience.

Instead, we should flip all of this around and follow the same pattern IO does: move the definitions of these methods to Resource itself as members (taking the appropriate implicit evidence for F individually), and then change the typeclass implementations to simply forward the call onto the appropriate member function. This is actually a pretty easy change, just a little tedious and time-consuming. It should help with the ergonomics quite considerably though.

[alexandrustana]

I could try and tackle this one

[joroKr21]

I thought the idea was to move the implementations themselves and forward to them from the type class like this:

trait Resource:
  def startOn(ec: ExecutionContext)(implicit F: Async[F]): Resource[F, Fiber[Resource[F, *], Throwable, A]] = ???
    // move implementation here

object Resource:
  implicit def asyncInstance[F[_]](implicit F: Async[F]) = new Async[Resource[F, *]] {
    def startOn[A](fa: Resource[F, A])(ec: ExecutionContext): Resource[F, Fiber[Resource[F, *], Throwable, A]] =
      fa.startOn(ec)