This commit allows the server-side form arch parser used in tests to
also include the "end_date_field" defined in the `options` attribute of
daterange widgets in the dictionnary of fields found in the arch.
The daterange widget is currently the only case where the client adds
another editable field dynamically in the list of known fields. This is
not ideal since the server does not know that when computing the initial
arch sent to the client. The workaround is to also include the
"end_date_field" in the arch with `invisible="1"`, and to add a special
case for the server-side form arch parser used in tests.
Ideally we would want a proper way to define field dependencies in the
arch, but since this widget here is the only use case for that feature
it is better for now to handle it in this simple, more naive way.
Part of task 3121497
closesodoo/odoo#112171
Related: odoo/enterprise#38569
Signed-off-by: Michaël Mattiello <mcm@odoo.com>