Made the new template.Context.flatten() method a public API.

That method was introduced in 9db4271bd1.

Refs #21765.

django/template/context.py

@@ -97,6 +97,15 @@ class BaseContext(object):
         new_context._reset_dicts(values)
         return new_context
 
+    def flatten(self):
+        """
+        Returns self.dicts as one dictionary
+        """
+        flat = {}
+        for d in self.dicts:
+            flat.update(d)
+        return flat
+
     def __eq__(self, other):
         """
         Compares two contexts by comparing theirs 'dicts' attributes.
@@ -104,13 +113,7 @@ class BaseContext(object):
         if isinstance(other, BaseContext):
             # because dictionaries can be put in different order
             # we have to flatten them like in templates
-            def flatten(dicts):
-                flat = {}
-                for d in dicts:
-                    flat.update(d)
-                return flat
-
-            return flatten(self.dicts) == flatten(other.dicts)
+            return self.flatten() == other.flatten()
 
         # if it's not comparable return false
         return False