[FIX] core: initialize new stored related field via SQL

Filling the new column in SQL is dramatically faster than doing it via
the ORM, which iterates over all the records in the table.

The test case is creating a related field for 100+ records with distinct
values.  Setting the field's value was taking more than 100 queries.  It
now takes 3 queries.

task-2449313
opw-2380445
opw-2389376
https://github.com/odoo/enterprise/pull/15910



closes odoo/odoo#65232

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>