The goal of this commit is to complete the list of activeFields for
an x2many in list mode when a record is opened with the fields present
in its form view. This ensures that there is always an activeField
for all the data in a record. Before this commit, when the x2many's
form view was not inline, when the form view was closed, the fields
not present in the list view no longer had an activeField, which could
cause crashes.
closesodoo/odoo#130453
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>