Fix for get-value with empty uninterpreted sort domain (#8547)

Fix for get-value with empty uninterpreted sort domain (#8547)

Alternative for https://github.com/cvc5/cvc5/pull/8546.

We were mistakenly using `mkGroundTerm` instead of `mkGroundValue` to make the domain of an uninterpreted sort non-empty.

This ensures that get-value calls do not throw a spurious exception when there is a declared uninterpreted sort and there are no terms of that sort.

As a result, this also required fixing a few further issues regarding how uninterpreted sort constants are printed in models, and fixing the expected results on 2 more regressions.