Statistics on instantiations per quantified formula. (#4719)

Statistics on instantiations per quantified formula. (#4719)

This adds a new print format for instantiations --print-instantiations=num, which prints the total number of instantations of quantified formulas. This count is user-context-dependent, which is in sync with the existing print-instantiation format (list).

It also simplifies and improves printing of Instantiation Tries.