[FIX] web: extend the fieldsInfo of a view with the origin view to evaluate extra fields

Suppose you are editing a SO to add a new line. Depending on the configuration,
a sale order line wizard may open (e.g. if packages are activated).
This wizard is a form view, opened from the tree view of the sale order lines.
We have commit 8e515693
that adds extra fields from the originating view.
(However it doesn't work if the other view is inlined, so we modify this part to
add the extra field even in this case.)
Then we need the field info from the origin view in the target view;
we do so by extending the former with the content of the latter.

opw 1904337

closes odoo/odoo#28441