[FIX] stock: planned transfer

- Create a product A tracked by lot
- From the Dashboard, create a 'Planned Transfer'
- Add product A, any quantity
- Click on "Mark as TODO"

It's now possible to edit the serial numbers, but it's impossible to set
any quantity in the move lines.

This is due to the remaining context key `planned_picking` which makes
`is_initial_demand_editable = True`. In this case, `qty_done` is
read-only in the view `view_stock_move_line_operation_tree`.

As a workaround, `action_confirm` returns an action and set the context
accordingly.

opw-785332

addons/stock/models/stock_picking.py

@@ -542,7 +542,19 @@ class Picking(models.Model):
         # call `_action_assign` on every confirmed move which location_id bypasses the reservation
         self.filtered(lambda picking: picking.location_id.usage in ('supplier', 'inventory', 'production') and picking.state == 'confirmed')\
             .mapped('move_lines')._action_assign()
-        return True
+        if self.env.context.get('planned_picking') and len(self) == 1:
+            action = self.env.ref('stock.action_picking_form')
+            result = action.read()[0]
+            result['res_id'] = self.id
+            result['context'] = {
+                'search_default_picking_type_id': [self.picking_type_id.id],
+                'default_picking_type_id': self.picking_type_id.id,
+                'contact_display': 'partner_address',
+                'planned_picking': False,
+            }
+            return result
+        else:
+            return True
 
     @api.multi
     def action_assign(self):