Breaking change: NestedSyntax collides with Optionable in Scalatest causing codebases to no longer compile tests.

[coltfred]

If you upgrade from cats 1.1.0 to 1.2+ and you use OptionValues from Scalatest you'll end up with errors like the following.

src/test/scala/com/ironcorelabs/admin/CookiesTest.scala:39: type mismatch;
 found   : gottenCookie.type (with underlying type Option[scodec.bits.ByteVector])
 required: ?{def value: ?}
Note that implicit conversions are not applicable because they are ambiguous:
 both method catsSyntaxNestedId in trait NestedSyntax of type [F[_], G[_], A](value: F[G[A]])cats.syntax.NestedIdOps[F,G,A]
 and method convertOptionToValuable in trait OptionValues of type [T](opt: Option[T])(implicit pos: org.scalactic.source.Position)CookiesTest.this.Valuable[T]
 are possible conversion functions from gottenCookie.type to ?{def value: ?}
      gottenCookie.value shouldBe Password(hexBytes.value)

This is caused by the fact that .value is syntax added to the Option type as well as the NestedSyntax conversion are at the same implicit level. I hadn't upgraded my cats version in a while so I didn't notice this until now, but it's a huge PITA. It means people might end up with cats all of a sudden not working for their project.

[kailuowang]

related issue #2514

[coltfred]

@kailuowang Should we close these on merge or when the release happens?

[kailuowang]

yeah we can close this one.