When returning a dropshipped and subcontracted product to an internal
location, the received quantity of the PO line will be incorrect

To reproduce the issue:
1. In Settings, enable "Storage Locations"
2. Create two storable products P_compo, P_Finished
3. Create a BoM:
    - Product: P_finished
    - Type: Subcontracting
    - Subcontractors: a subcontractor S
    - Components: 1 x P_compo
4. In Locations, edit WH/Stock:
    - Return location: True
5. Create and confirm a PO:
    - Vendor: S
    - Deliver To: Dropship
    - Drop Ship Address: a partner P
    - Products: 1 x P_finished
6. Validate the receipt
7. Create a return with 1 x P_finished:
    - Update SO/PO quantities: True
    - Return Location: WH/Stock
8. Validate the return
9. Go back to the PO

Error: The qty received is 2, it should be 1 (it should not be 0 since
the product has been returned to an internal location)

In `/purchase_stock._compute_qty_received`, there is already a code to
anticipate such a situation (i.e., a user who returns a dropshipped
product to his stock location):
https://github.com/odoo/odoo/blob/bf3c398f0644f690c64815b2b6e298aed7bedd70/addons/purchase_stock/models/purchase.py#L300-L305
However, the methods `_is_dropshipped` and `_is_dropshipped_returned` do
not include the feature subcontracting + dropshipping. This is the
reason why, in `_compute_qty_received`, the above condition is not
respected and why we add the return stock move to the received qty.

OPW-3030895

Part-of: odoo/odoo#105185