Have a list view with a many2many field, and an onchange on a
field in the list that returns a command 5 (CLEAR, or DELETE_ALL
in the js terminology). Before this commit, the command 5 was
mapped to a list of commands 2 (DELETE), i.e. all records in the
many2many relation were deleted when the record was saved. We
instead want those records to be removed from the relation, i.e.
the command 5 should be mapped to a list of command 3 (UNLINK, or
FORGET in the js terminology).

Note that this only impacts list and kanban views, as the form
view still used the BasicModel.

Issue reported here https://github.com/odoo/odoo/commit/48ef812a635f70571b395f82ffdb2969ce99da9e#r126483773



closes odoo/odoo#134318

Signed-off-by: Francois Georis (fge) <fge@odoo.com>