[FIX] base, test_new_api: adapt generated default form view to Grid

When we changed the display of the form in v16, we forgot to adapt the
python framework default form view layout (used when the form view of
the model isn't defined). This provided a weird layout in these case on
Odoo 16.+.

To fix this bad behavior, we adapt the algorithm used to build the
default view form.

Steps to reproduce:
Create a model without a form view and edit it (like we do when you
follow the rd training).

closes odoo/odoo#132228

Signed-off-by: Pierre Paridans (app) <app@odoo.com>