[FIX] web: introduce format for many2one_reference for form view

The format of `many2one_reference` was not introduced when the new field type
was created, which leads to empty values when the web client is trying to
display the value of such fields in form views.

Since the value of this field is an ID, it is decided to display it like an
integer, which is consistent with previous behavior: the fields that are now
`many2one_reference` are still stored as integer and they were already displayed
as integer before.

This was fixed in list views in commit d0c852f50e
and the current commit fixes it for form views.

opw-2127010
closes #38009

closes odoo/odoo#41666

X-original-commit: c37a16c9dfd09038925034b90ab49e1ab674e714
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/web/static/src/js/fields/field_registry.js

@@ -61,7 +61,8 @@ registry
     .add('toggle_button', basic_fields.FieldToggleBoolean)
     .add('dashboard_graph', basic_fields.JournalDashboardGraph)
     .add('ace', basic_fields.AceEditor)
-    .add('color', basic_fields.FieldColor);
+    .add('color', basic_fields.FieldColor)
+    .add('many2one_reference', basic_fields.FieldInteger);
 
 // Relational fields
 registry