[FIX] base, web: transfer readonly/required modifiers for kanban/tree

Since odoo/odoo@69c3d5aa25655173ed66a52570559322c650c7df
the readonly and required modifiers were no longer passed
for non-editable views. Which means:
- kanban: never passed,
- tree: passed only when `editable="1"` or `multi_edit="1"`,
- form: always passed.

The rationale behind that is that a view which is considered
as readonly doesn't need to know if its field are readonly or required,
as by definition, if the view is readonly, the user shouldn't
be able to modify anything in the view.
This was to make the views sent to the web client more light-weight,
not sending unused information, and save KB of transfers.

However, some widgets, used in the kanban and non-editable tree,
allow to modify fields, even in readonly considered views,
and therefore need to know these readonly/required modifiers
from the field definition in the Python model.

e.g. the `widget="color"`, odoo/odoo#103478

Ideally, these readonly/required modifiers should be transferred
only when the widget requires it, to avoid transferring the
readonly/required modifiers
when they are not useful in kanban/tree views
(which is 99% of the time).
However, this would require a bigger refactoring,
which is considered too risky compared to the added value
for a stable release.

task-3013110

closes odoo/odoo#106766

Signed-off-by: Denis Ledoux (dle) <dle@odoo.com>