Polysat updates (#5444)

* Simplify adding lemmas

* Remove misleading constructor from tmp_assign.

The idea is that tmp_assign is only created on the stack and
short-lived.  Instead of having a convenience constructor that takes a
constraint_ref, it's clearer to have an explicit .get() at the call
site.

* Remove some log messages

* bugfix

* fix

* Add stub for conflict_core

* wip

* Add example by Clemens

src/math/polysat/constraint.cpp

@@ -151,8 +151,9 @@ namespace polysat {
 
     std::ostream& constraint::display_extra(std::ostream& out) const {
         out << " @" << level() << " (b" << bvar() << ")";
-        if (is_undef())
-            out << " [inactive]";
+        if (is_positive()) out << " [pos]";
+        if (is_negative()) out << " [neg]";
+        if (is_undef()) out << " [inactive]";
         return out;
     }