fix(prefer-to-have-class): support direct elements

[YodHeVauHe]

Fixes #490.

prefer-to-have-class returned early unless the receiver was a Testing Library query, so expect(document.body).toHaveAttribute('class', …) was never reported. The guard now also allows a direct element.

npm test -- --runInBand passed: 12 suites, 621 tests. npm run lint passed.

[G-Rath]

While this looks to address what the OP described (and I think would be my preference at this point), that issue brought up

1. we're inconsistent across our rules around this (and consistency is a goal)
2. not having the check apparently caused a lot of false positives for some reasons in codebases

at this point I'd like more data before committing to a direction, as we've only heard from one user