Debug instantiations output (#4739)

Debug instantiations output (#4739)

This prints # instantiations per round (during solving) for each quantified formula with `--debug-inst`, giving output like this:
```
(num-instantiations myQuant1 1)
(num-instantiations myQuant2 1)
unsat
```

It also changes the default value of print-inst-full to match the behavior of unsat-cores vs unsat-cores-full (by default, nameless quantifiers are ignored).

It fixes an issue with qid, where mkVar was accidentally used instead of mkConst, leading to assertion failures in debug.  Marking major since this fixes debug regress1.