Polysat: check test results, forbidden intervals for coefficient -1 (#5241)

* Use scoped_ptr for condition

* Check solver result in unit tests

* Add test for unusual cjust

* Add solver::get_value

* Broken assertion

* Support forbidden interval for coefficient -1

src/math/polysat/solver.h

@@ -272,6 +272,11 @@ namespace polysat {
          */
         pdd var(pvar v) { return m_vars[v]; }
 
+        /**
+         * Return value of v in the current model (only meaningful if check_sat() returned l_true).
+         */
+        rational get_value(pvar v) const { SASSERT(!m_justification[v].is_unassigned()); return m_value[v]; }
+
         /**
          * Create polynomial constraints (but do not activate them).
          * Each constraint is tracked by a dependency.