QuerySet.update() : return the IDs of the matched rows

[Дилян Палаузов]

By coincidence all backends that can_return_ids_from_bulk_insert, which happens to be only Postgresql, can also return ids from UPDATE:

UPDATE ... SET ... RETURNING id;

• update QuerySet.update() to return the PKs of the updated rows
• update the documentation of QuerySet.update(), stating the specific return type for PG
• possibly rename can_return_ids_from_bulk_insert to can_return_ids or can_return_anything(_from_select_insert_update_delete)?