replace restore_size_trail by more generic restore_vector

other updates:
- change signature of advance_qhead to simplify call sites
- have model reconstruction replay work on a tail of dependent_expr state, while adding formulas to the tail.

src/ast/simplifiers/max_bv_sharing.cpp

@@ -261,7 +261,7 @@ public:
             m_fmls.update(idx, dependent_expr(m, new_curr, d));            
         }
         m_rw.cfg().cleanup();
-        advance_qhead(m_fmls.size());
+        advance_qhead();
     }        
 };