Implement kind projector's functionality directly

[biboudis]

We already accept both _ and ? as a wildcard. Following kind projector, we should now accept * as a parameter placeholder for a type lambda.

[smarter]

Note that this should be guarded by the (already existing) -Ykind-projector, which I think should also support the other syntaxes for type lambdas implemented by kind-projector to ease cross-compilation:

Lambda[A => (A, A)]
λ[A => (A, A)]
λ[(+[A], +[B]) => Either[A, B]]
λ[(`+A`, `+B`) => Either[A, B]]

See https://github.com/typelevel/kind-projector

[travisbrown]

For what it's worth we could very easily live without kind-projector's variance syntax in Cats (see this PR for the change), and in all of the other Typelevel or Typelevel-adjacent projects I just checked.

I currently have a -Ykind-projector implementation for * and am working on λ[A => ...], and am hoping to have a PR ready early next week, but I personally don't see supporting kind-projector's -* or the backticked variance stuff as a priority.