Re-implement `nextPrimeInteger` predicate (#9281)

This also adds `nextPrimeWord#` and `nextPrimeBigNat` predicates.

`nextPrimeInteger` has been available since `integer-gmp-0.5.1`
(added via f49735486533842cc84df70cafc8d565dffd75db).
Re-activate `integerGmpInternals` test (#9281)

The `integerGmpInternals` test was disabled in
c774b28f76ee4c220f7c1c9fd81585e0e3af0e8a as many of the primitives
tested in that test weren't available yet w/ `integer-gmp2`.

However, most operations have been reimplemented by now, with the
exception of

    recipModInteger  :: Integer -> Integer -> Integer
    gcdExtInteger    :: Integer -> Integer -> (Integer, Integer)
    powModSecInteger :: Integer -> Integer -> Integer -> Integer
    powModInteger    :: Integer -> Integer -> Integer -> Integer
    powInteger       :: Integer -> Word -> Integer

which are still missing, and will (time permitting) be reimplemented
over time.