fix ambiguity checks in ZLayer#provide macro

[myazinn]

Zlayer#provide* macro family sometimes allows having duplicate layers for the same dependency. Here's an example

trait Repository {
  def upsert(data: Any): UIO[Unit]
}

case class MongoRepository() extends Repository {
  override def upsert(data: Any): UIO[Unit] = ZIO.unit
}
object MongoRepository {
  val live: ULayer[MongoRepository] = ZLayer.fromFunction(MongoRepository.apply _)
}

case class GreenplumRepository() extends Repository {
  override def upsert(data: Any): UIO[Unit] = ZIO.unit
}
object GreenplumRepository {
  val live: ULayer[GreenplumRepository] = ZLayer.fromFunction(GreenplumRepository.apply _)
}

case class RepositoryLive(mongo: MongoRepository, gp: GreenplumRepository) extends Repository {
  override def upsert(data: Any): UIO[Unit] = mongo.upsert(data) <&> gp.upsert(data)
}
object RepositoryLive {
  val live: URLayer[MongoRepository with GreenplumRepository, RepositoryLive] = ZLayer.fromFunction(RepositoryLive.apply _)
}

In the above example we've got three different repository implementations, one of which is a combination of two of them.
If we use them like this

ZIO.service[Repository].provide(RepositoryLive.live, MongoRepository.live, GreenplumRepository.live)

The code will compile fine without any warnings. Though it will do an expected thing (it will actually construct and use RepositoryLive), this is quite unexpected since any of three layers could've been used. If we just change their order like this

ZIO.service[Repository].provide(MongoRepository.live, RepositoryLive.live, GreenplumRepository.live)

then it will produce a warning that RepositoryLive.live and GreenplumRepository.live are unused. But overall I'd say that in this case the behaviour is undefined and should be allowed. That's why this MR exists ¯_(ツ)_/¯

[myazinn]

This feels like a stupid hack, but without it the code in this repo (and I assume in many other places) won't compile. It fails with an ambiquity error zio.ZAny is provided by: which looks like some Scala type inference issue, since type ZAny >: Any.
So here we just throw away any type for which Any <:< tpe is true (including Any apparently).

[adamgfraser]

Thank you! 🙏