When ir.values was removed and the "action" ir.values were merged
directly into the actions themselves, "client_action_relate" was
discarded as unused (and possibly too similar to
client_action_multi?). *However*:
* it was actually used implicitly as "relate" was the default key2 of
the <act_window> XML tag
* and it had a crucial difference from client_action_multi:
client_action_multi is shown on both form and list views by default
and only on list if multi=True, whereas relate is shown on *either*
the form or list view (tree if multi else form)
This means without relate the actions which should be only visible on
the form view are now on both list and tree, which leads to
overpopulated `Action` menus and odd behaviours (e.g. actions relying
active_id on lists, which id do they get and why?)
=> reintroduce relate as "action_form_only" for the specific case of
multi=False and either no key2 or a key2 of client_action_relate. If
multi=True then binding_type=action.
Fixes#20124
Followup: Task 1843603 to remove #multi and redundancy
xmo-odoo
020906659e