🧪 Testing: Rename "mutation" tests to "integration"

[JoshuaKGoldberg]

Overview

I originally named "mutation" tests in this library and auto-mutate/automutate-tests as such because they were testing "mutators". The naming all made sense.

But, "mutation testing" is separately a thing! https://stryker-mutator.io. IMO it's confusing to use the phrase in a way different from the industry norm.

Proposal: let's switch the name for the concept in this repo to... say, integration tests? That's basically what they are, I think. WDYT @rubiesonthesky?

[rubiesonthesky]

I think integration tests make sense. I'm favor of that!

I also think that separate end to end tests would be great! But let's wait with that until monorepo support.

Edit: haha #1506 , you already made task about that :)

[rubiesonthesky]

Would you think it would make sense to rename folder test to integrationTests? I would also move the testSetup.ts file there so they are all together.

[JoshuaKGoldberg]

Ehhh I'm not a fan of long folder names in the root. IME it gets annoying and inconvenient to work with. test is a pretty common standard - let's stick with it IMO.