Add formik to the user suite

[weswigham]

Formik's .d.ts typechecks on its own now, however its example fails. There are two compounding reasons for this. The first is that formik's type parameters for its tag do not have an inference site for Values, so it becomes the default. This can be fixed in formik by replacing the type parameter declarations (Props extends FomikConfig<Values> = FormikConfig<Values>, Values = object) with ExtraProps = {}, Values = object and everywhere Props is referenced today, instead writing FormikConfig<Values> & ExtraProps. That would be how you can achieve the desired inferences for an equivalent call, anyway. Which leads me to the second reason: In JSX, this pattern is presently broken because our JSX type calculation code aggressively gets the apparent type of types it uses to construct the attributes type - contrary to what we'd like for appropriate contextual typing (since the apparent type replaces type parameters with their constraints, preventing us from drawing inferences). I've put a PR up to fix that at #21383, but quickinfo is can still be wrong because of #21382.