Fields can now be marqued as required inside a field definition. If the field
value is `undefined` or updated to `undefined`, an error will be throw.
```
stringifiedDomain: attr({
default: '[]',
required: true,
}),
```
task-2323665
closes odoo/odoo#59094
Related: odoo/enterprise#13883
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>