[18.0][OU-FIX] account: fill company_id and journal_id for all existing payments

[eantones]

At 18.0 account.payment stops delegating to its move (_inherits dropped) and journal_id / company_id become the payment's own stored required fields (both compute=..., store=True, required=True).

The current fill_account_payment():

• sets journal_id from the move only when the move's journal is of type bank/cash/credit — payments whose move lives in any other journal type (e.g. general, common for netting/compensation flows) are left with journal_id = NULL;
• never sets company_id at all (the analogous fill_statement_line_fields() does fill it for statement lines).

Consequences on a real 14→18 chain (measured on a production-size database: 164,706 payments):

• company_id NULL on 119,930 rows (73%) and journal_id NULL on 38,968 → unable to set NOT NULL on column company_id/journal_id at load, so both required columns end up without their NOT NULL constraint;
• with standard multi-company record rules, company_id = NULL payments behave as shared records, visible from every company;
• worse, _compute_company_id() falls back to self.env.company — the first user who edits a legacy payment silently stamps their own active company on it.

Both values are fully derivable from the payment's move (move_id and move.company_id are never NULL for legacy payments). This patch:

• adds the account.payment.company_id column in pre (it did not exist in ≤17.0) and fills it from the move for every payment;
• falls back to the move's journal for payments whose move sits outside bank/cash/credit journals, so historical rows keep their true journal.

After the fill, both SET NOT NULL succeed and the schema warnings disappear.