Small polysat fixes (#5183)

* Add some display functions

* Add new variables to free vars

src/math/polysat/justification.cpp

@@ -0,0 +1,29 @@
+/*++
+Copyright (c) 2021 Microsoft Corporation
+
+Module Name:
+
+    polysat justification
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2021-03-19
+
+--*/
+
+#include "math/polysat/justification.h"
+
+namespace polysat {
+
+    std::ostream& justification::display(std::ostream& out) const {
+        switch (kind()) {
+        case justification_k::unassigned:
+            return out << "unassigned";
+        case justification_k::decision:
+            return out << "decision (level " << level() << ")";
+        case justification_k::propagation:
+            return out << "propagation (level " << level() << ")";
+        }
+    }
+
+}