Add simplification customization for SMTLIB2

Add the ability to customize incremental pre-processing simplification for the SMTLIB2 front-end. The main new capability is to use pre-processing tactics in incremental mode that were previously not available. The main new capabilities are
- solve-eqs
- reduce-args
- elim-unconstrained
There are several more. Documentation and exposed simplifiers are populated incrementally. The current set of supported simplifiers can be inspected by using z3 with the --simplifiers flag or referring to https://microsoft.github.io/z3guide/docs/strategies/simplifiers

Some pending features are:
- add the ability to update parameters to simplifiers similar to how tactics can be controlled using parameters.
- expose simplification solvers over the binary API.

src/cmd_context/cmd_context.h

@@ -318,7 +318,7 @@ protected:
     void register_builtin_ops(decl_plugin * p);
     void load_plugin(symbol const & name, bool install_names, svector<family_id>& fids);
     void init_manager_core(bool new_manager);
-    void init_manager();
+
     void init_external_manager();
     void reset_cmds();
     void finalize_cmds();
@@ -414,7 +414,9 @@ public:
     sexpr_manager & sm() const { if (!m_sexpr_manager) const_cast<cmd_context*>(this)->m_sexpr_manager = alloc(sexpr_manager); return *m_sexpr_manager; }
 
     proof_cmds* get_proof_cmds() { return m_proof_cmds.get(); }
+    void init_manager();
     solver* get_solver() { return m_solver.get(); }
+    void set_solver(solver* s) { m_solver = s; }
     void set_proof_cmds(proof_cmds* pc) { m_proof_cmds = pc; }
 
     void set_solver_factory(solver_factory * s);