Add ApplicativeThrow and MonadThrow to cats package object (from cats-effect)

[agustafson]

I noticed that the ApplicativeThrow and MonadThrow type aliases had been added to cats-effect:
https://github.com/typelevel/cats-effect/blob/series/2.x/core/shared/src/main/scala/cats/effect/package.scala#L41-L43

I felt that it made more sense for it to be cats as ApplicativeError and MonadError are in cats rather than cats-effect.

Also, it seems like ApplicativeThrow has erroneously had an unused A type param added, so I figured it was best to remove it. I'm not sure if that will clash or cause problems if both cats._ and cats.effect._ are imported. I'll open a separate PR against cats-effect 2.x branch to remove the A

This is a kind reminder to run sbt +prePR and commit the changed files, if any, before submitting.

As an aside, I tried running this task but it failed on master as well as my PR, but the code all seems to be formatted correctly.

[codecov-io]

Codecov Report

Merging #3696 (d9b8c79) into master (ba70c8c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3696   +/-   ##
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  Coverage   90.23%   90.23%           
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  Files         391      391           
  Lines        8861     8861           
  Branches      242      242           
=======================================
  Hits         7996     7996           
  Misses        865      865           

[agustafson]

It'd also be kinda nice if we could add a

object MonadThrow {
  def apply[F[_]](implicit ev: MonadThrow[F]): MonadThrow[F] = ev
}

but wasn't sure where we might put that

[bplommer]

If/when this is released I'd suggest we remove these from CE3 and change the ones in CE2 to be aliases for these.

[bplommer]

It'd also be kinda nice if we could add a

object MonadThrow {

  def apply[F[_]](implicit ev: MonadThrow[F]): MonadThrow[F] = ev

}

but wasn't sure where we might put that

Good idea - I think it could either go directly below the alias or in a package cats {} block in the same file directly below the package object

[agustafson]

It'd also be kinda nice if we could add a

object MonadThrow {

  def apply[F[_]](implicit ev: MonadThrow[F]): MonadThrow[F] = ev

}

but wasn't sure where we might put that

Good idea - I think it could either go directly below the alias or in a package cats {} block in the same file directly below the package object

Yeah, I wondered if putting it in the same file as ApplicativeError/MonadError made sense as an alternative. Just so that the package object didn't get too crowded.

[LukaJCB]

I like it 👍

[djspiewak]

I like this a lot. So much better than having it in Cats Effect