[IMP] *: M2X search/add popup should display a kanban instead of a list in mobile

- Add support of "kanban_view_ref" on many2x fields:
For many2one fields, this specific kanban view will be opened when you click
on this field. Note that in desktop, the behavior stay unchanged:
'Search More' will open the tree view.
For many2many fields, this specific kanban view will be opened when you add
a record in mobile.

- Add support "selection_mode" in kanban views.
This boolean is set to true when you want to use a kaban view to
select a record instead of open a record.
"selection_mode" is now passed in qweb_context to allow developers
to use t-if='selection_mode' in kanban views to show or hide elements;
buttons, dropdowns, anchor tags are not necessary when selection_mode
is enabled. So those elements can be hidden based on this condition.
Useful when kanban view is opened from m2o in mobile environment.

Task ID : 1924779

closes odoo/odoo#30747

Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>