CNF conversion refactoring (#5547)

* split sat2goal out of goal2sat

These two classes need different things out of the sat::solver class,
and separating them makes it easier to fiddle with their dependencies
independently.

I also fiddled with some headers to make it possible to include
sat_solver_core.h instead of sat_solver.h.

* limit solver_core methods to those needed by goal2sat

And switch sat2goal and sat_tactic over to relying on the derived
sat::solver class instead. There were no other uses of solver_core.

I'm hoping this makes it feasible to reuse goal2sat's CNF conversion
from places like the tseitin-cnf tactic, so they can be unified into a
single implementation.

src/sat/smt/sat_internalizer.h

@@ -0,0 +1,35 @@
+/*++
+Copyright (c) 2020 Microsoft Corporation
+
+Module Name:
+
+    sat_internalizer.h
+
+Abstract:
+
+    Header for SMT theories over SAT solver
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2020-08-25
+
+--*/
+#pragma once
+
+#include "util/sat_literal.h"
+
+namespace sat {
+    class sat_internalizer {
+    public:
+        virtual ~sat_internalizer() {}
+        virtual bool is_bool_op(expr* e) const = 0;
+        virtual literal internalize(expr* e, bool learned) = 0;
+        virtual bool_var to_bool_var(expr* e) = 0;
+        virtual bool_var add_bool_var(expr* e)  = 0;
+        virtual void cache(app* t, literal l) = 0;
+        virtual void uncache(literal l) = 0;
+        virtual void push() = 0;
+        virtual void pop(unsigned n) = 0;
+        virtual void set_expr2var_replay(obj_map<expr, sat::bool_var>* r) = 0;
+    };
+}