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/ast/simplifiers/rewriter_simplifier.h

@@ -53,3 +53,7 @@ public:
     void updt_params(params_ref const& p) override { m_params.append(p); m_rewriter.updt_params(m_params); }
     void collect_param_descrs(param_descrs& r) override { th_rewriter::get_param_descrs(r); }
 };
+
+/*
+  ADD_SIMPLIFIER("simplify", "apply simplification rules.", "[](auto& m, auto& p, auto &s) -> dependent_expr_simplifier* { return alloc(rewriter_simplifier, m, p, s); }")
+ */