This commit aims to make unit tests pass when creating a new database
with only 'survey' installed.
The tour 'test_survey' was not loaded before reaching /survey/start,
causing tests to fail.
The js asset is now loaded within web.assets_common because the tour
should also work with the 'public' user. For this reason,
'web.assets_backend' is not a good fit.
Widget 'root.widget' was undefined too. Appropriate js file is now
loaded.
Closes#33330
Signed-off-by: Christophe Simonis <chs@odoo.com>