[FIX] web: no error on single active_ids state load

In eg. 13.0 when refreshing sales analysis action of a product, we would
get an error because we have a single active_ids which is not expected
by the code.

With this commit, we use .toString() on the jQuery BBQ parsed active_ids
as it was done before 32b8cec5 refactoring (january 2018).

The added test with the fix fails with an error:

  TypeError: state.active_ids.split is not a function
  at Class.loadState (/web/static/src/js/chrome/action_manager_act_window.js)

opw-2471982

closes odoo/odoo#70226

X-original-commit: a8c731092b7aa95bca46f56f6c069e1c1a8a2292
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>
Co-authored-by: Nicolas Lempereur <nle@odoo.com>