[doc] update 3.21 release notes

[devtools] Sort _cw_fields in fake_form Try to generate a predictable string, to help testing with PYTHONHASHSEED=random.

[entity] sort fetchattrs when generating rql Try to generate a predictable rql query, to help testing with PYTHONHASHSEED=random.

Update hgignore for temporary test databases

[js] removed unused and broken SuggestForm Widget (closes #5213487)

[test] Fix unittest_i18n to run properly with "pytest -t" (closes #5576169) When running "pytest -t", many tests modules will be imported and run within a single python process. unittest_i18n fails when run after tests such as unittest_webtest.py or unittest_httptest.py. The main reason is that unittest_i18n does various tricks to add a test cube to the search path, which badly fails when a previous test module has already loaded "stuff" (for lack of a better word). Instead, let's just call the 'i18ncube' command with subprocess. The change from logilab.common.testlib to unittest is not directly needed, but comes as a free cleanup with the above changes.

[server/test] fix random error in unittest_security When entering a new Connection, we cache the user and its 'login' attribute (with no permissions checking). This test makes 'CWUser.login' unreadable by guests, and then proceeds to make sure the 'anon' user can actually not read any 'login' attribute. However, due to the above cnx initialization, anon's login is actually cached, hence readable. This happens to make the test fail sometimes depending on the order in which CWUser entities are returned, because one of them has .complete() called, which as a side effect sets the attribute cache to None for unreadable attributes. Call .complete() on both entities to reset the login cache. While this is still highly debatable, at least it's consistent.

[entity] fix typo in comment

[doc] Add a tutorial and extend documentation for ExtEntityImporter Related to #5414753.

[dataimport] introduce the importer and extentity classes This introduces the ``ExtEntity`` class which is a transitional state between data at external source and the actual CubicWeb entities. ``ExtEntitiesImporter`` is then in charge to turn a bunch of ext entities into CW entities in repository, using a given store. This changeset also introduces ``SimpleImportLog`` and ``HTMLImportLog`` which implement the CW DataImportLog interface in order to show log messages in UI using simple text and HTML formats respectively, instead of storing these messages in database. Both have mostly been backported from cubes.skos.dataimport. Closes #5414753.