experimental feature to access congruence closure of SimpleSolver

This update includes an experimental feature to access a congruence closure data-structure after search.
It comes with several caveats as pre-processing is free to eliminate terms. It is therefore necessary to use a solver that does not eliminate the terms you want to track for congruence of. This is partially addressed by using SimpleSolver or incremental mode solving.

```python
from z3 import *
s = SimpleSolver()
x, y, z = Ints('x y z')
s.add(x == y)
s.add(y == z)
s.check()
print(s.root(x), s.root(y), s.root(z))
print(s.next(x), s.next(y), s.next(z))
```

src/api/python/z3/z3.py

@@ -7241,6 +7241,22 @@ class Solver(Z3PPObject):
         cube are likely more useful to cube on."""
         return self.cube_vs
 
+    def root(self, t):
+        t = _py2expr(t, self.ctx)
+        """Retrieve congruence closure root of the term t relative to the current search state
+        The function primarily works for SimpleSolver. Terms and variables that are
+        eliminated during pre-processing are not visible to the congruence closure.
+        """
+        return _to_expr_ref(Z3_solver_congruence_root(self.ctx.ref(), self.solver, t.ast), self.ctx)
+
+    def next(self, t):
+        t = _py2expr(t, self.ctx)
+        """Retrieve congruence closure sibling of the term t relative to the current search state
+        The function primarily works for SimpleSolver. Terms and variables that are
+        eliminated during pre-processing are not visible to the congruence closure.
+        """
+        return _to_expr_ref(Z3_solver_congruence_next(self.ctx.ref(), self.solver, t.ast), self.ctx)
+
     def proof(self):
         """Return a proof for the last `check()`. Proof construction must be enabled."""
         return _to_expr_ref(Z3_solver_get_proof(self.ctx.ref(), self.solver), self.ctx)