Cache: compute cache id in a deterministic way

by using str on a dict we don't produce consistent results depending
on hash randomization. This was visible with erp5_core_test:testCacheTool
and PYTHONHASHSEED 12 , the cache id generated in
https://lab.nexedi.com/nexedi/erp5/-/blob/a0aa9184d/bt5/erp5_core_test/TestTemplateItem/portal_components/test.erp5.testCacheTool.py#L216-218
was
"('py_script_obj', (60000,), {'result': 'a short value', 'portal_path': ('', 'erp5')})"

and the cache id generated in
https://lab.nexedi.com/nexedi/erp5/-/blob/a0aa9184d/bt5/erp5_core_test/TestTemplateItem/portal_components/test.erp5.testCacheTool.py#L239-241
with same arguments for delete was
 "('py_script_obj', (60000,), {'portal_path': ('', 'erp5'), 'result': 'a short value'})")

product/ERP5Type/Cache.py

@@ -225,11 +225,11 @@ class CachingMethod:
     ## generate cache id out of arguments passed.
     ## depending on arguments we may have different
     ## cache_id for same method_id
-    return str((method_id, args, kw))
+    return str((method_id, args, sorted(kw.items())))
 
   @staticmethod
   def erasable_cache_id_generator(method_id, obj, *args, **kw):
-    return str((method_id, obj.getCacheCookie(method_id), args, kw))
+    return str((method_id, obj.getCacheCookie(method_id), args, sorted(kw.items())))
 
   def __init__(self, callable_object, id, cache_duration=180,
                cache_factory=DEFAULT_CACHE_FACTORY,