Define explicitly escape char used for like operators

For now we rely on the default value set by python-sql but SQL-92 does not
define a default value.

Closes #12933
(grafted from 659160cd1681a6a1bc98d51a97d7765ee8d31714)

--HG--
branch : 7.0

trytond/trytond/model/fields/field.py

@@ -1,7 +1,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 import warnings
-from functools import wraps
+from functools import partial, wraps
 
 import sql
 from sql import (
@@ -234,10 +234,10 @@ def order_method(func):
 SQL_OPERATORS = {
     '=': operators.Equal,
     '!=': operators.NotEqual,
-    'like': operators.Like,
-    'not like': operators.NotLike,
-    'ilike': operators.ILike,
-    'not ilike': operators.NotILike,
+    'like': partial(operators.Like, escape='\\'),
+    'not like': partial(operators.NotLike, escape='\\'),
+    'ilike': partial(operators.ILike, escape='\\'),
+    'not ilike': partial(operators.NotILike, escape='\\'),
     'in': operators.In,
     'not in': operators.NotIn,
     '<=': operators.LessEqual,