[FIX] stock: Improve date_deadline propagation

The date_deadline propagation would update the sale records multiple times depending on some configuration (check example below).
This happens because 'already_propagate_ids' is copied at the beginning of _set_date_deadline (set | set = new set).
So, when a child move propagates to multiple other moves, it is not known by the parent move, which will redo the propagation.

To prevent this, we always keep the same reference for 'already_propagate_ids' (context: 'date_deadline_propagate_ids'). This means that a parent and child move share the exact same Set, and when the child move updates the Set, it also updates the parent Set.
So when a child move propagates, the parent will know which moves have been done.

   MOVES LINKAGE
       Move B
      /   |   \
  Move A  |  Move D
      \   |   /
       Move C

PROPAGATION GRAPHS:
  BEFORE    |  AFTER
------------+--------
    A       |    A
  /   \     |    |
  C   B     |    B
 / \ / \    |    |
 B D C D    |    C
 | | | |    |    |
 D B D C    |    D
------------+--------
    11      |    4     NUMBER OF CALLS

OPW-3904178

closes odoo#164734

Signed-off-by: Arnold Moyaux (arm) <arm@odoo.com>
Co-authored-by: Mathieu Walravens <wama@odoo.com>

addons/stock/models/stock_move.py

@@ -464,7 +464,8 @@ def key_virtual_available(move, incoming=False):
 
     def _set_date_deadline(self, new_deadline):
         # Handle the propagation of `date_deadline` fields (up and down stream - only update by up/downstream documents)
-        already_propagate_ids = self.env.context.get('date_deadline_propagate_ids', set()) | set(self.ids)
+        already_propagate_ids = self.env.context.get('date_deadline_propagate_ids', set())
+        already_propagate_ids.update(self.ids)
         self = self.with_context(date_deadline_propagate_ids=already_propagate_ids)
         for move in self:
             moves_to_update = (move.move_dest_ids | move.move_orig_ids)