convert reduce-args to a simplifier

- convert reduce-args to a simplifier. Currently exposed as reduce-args2 tactic until the old tactic code gets removed.
- bug fixes in model_reconstruction trail
  - allow multiple defs to be added with same pool of removed formulas
  - fix tracking of function symbols instead of expressions to filter replay
- add nla_divisions to track (cheap) divisibility lemmas.
-

src/math/lp/nla_solver.h

@@ -25,6 +25,7 @@ namespace nla {
         core* m_core;
     public:
         void add_monic(lpvar v, unsigned sz, lpvar const* vs);    
+        void add_idivision(lpvar r, lpvar x, lpvar y);
         solver(lp::lar_solver& s, reslimit& limit);
         ~solver();
         nla_settings& settings();