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/simplifier_cmds.h

@@ -0,0 +1,42 @@
+/*++
+Copyright (c) 2023 Microsoft Corporation
+
+Module Name:
+
+    simplifier_cmds.h
+
+Abstract:
+    Support for simplifier commands in SMT 2.0 front-end
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2023-01-30
+
+--*/
+#pragma once
+
+#include "ast/ast.h"
+#include "ast/simplifiers/dependent_expr_state.h"
+#include "util/params.h"
+#include "util/cmd_context_types.h"
+#include "util/ref.h"
+
+
+class simplifier_cmd {
+    symbol             m_name;
+    char const *       m_descr;
+    simplifier_factory m_factory;
+public:
+    simplifier_cmd(symbol const & n, char const * d, simplifier_factory f):
+        m_name(n), m_descr(d), m_factory(f) {}
+
+    symbol get_name() const { return m_name; }
+    
+    char const * get_descr() const { return m_descr; }
+    
+    simplifier_factory factory() { return m_factory; }
+};
+
+simplifier_factory sexpr2simplifier(cmd_context & ctx, sexpr * n);
+
+void install_core_simplifier_cmds(cmd_context & ctx);