Make cats-kernel law organization consistent with cats-core

[adelbertc]

No description provided.

[kailuowang]

related comment here #1341 (comment)

[LukaJCB]

I know, I just wrote the law testing guide that documented this inconsistency, but going forward I'd love to have these be consistent. So we are going to break bin-compat one last time before potentially a year or something, so now seems to be a good time, right?

[kailuowang]

On the other hand it's less big a deal to break bin compat in the laws module.

[LukaJCB]

I'm going to try to make a PR early next week :)

[johnynek]

I think keeping kernel very compatible is still important. Laws less so in my opinion. You don't transitively pull testing packages generally.