Make sure type literals aren't negative (#8306)

As Krzysztof pointed out in #8306, with NegativeLiterals and DataKinds,
definitions such as:

  type T = -1

were accepted, although type literals must be greater than zero.

Signed-off-by: Austin Seipp <austin@well-typed.com>
s/TypeNats/DataKinds/ in release notes.

Signed-off-by: Austin Seipp <austin@well-typed.com>