This commit implements a way for user to manually set a default value
for the `invoice_cash_rounding_id` field in moves, and apply by default
a standard `account.cash.rounding` record based on the found `ir.default`
record or the ISO-4217 standard for every available currency.

It adds 5 new `account.cash.rounding` record included on the data of the
`account` module. They're set with the 'biggest_tax' strategy so that
the user doesn't need to add required account data on the fields.

We use the `ir.default` object to store the "preferred" default value of
the move rounding field. The rounding field will also be computed to
make sure it gets filled with the default value. An override on
`default_get` is needed so that the default `ir.default` behavior does
not interferre with the compute and making sure the rounding field gets
computed correctly.

To set a preferred `ir.default` on the cash rounding field, the user
must create a new record on "User-Defined Defaults" menu, select the
cash rounding, fill the JSON value with the rounding record ID, and fill
either the company field and/or the condition string with
"currency=<currency_name>" (e.g. "currency=USD"). When searching through
the `ir.default` records to apply, the code will by priority search
through the record sorted by:

- company and currency condition filled
- currency condition filled
- company filled

By default, 3 `ir.default` record are created when installing `account`
module as an exception to the ISO-4217 standard in Odoo for the currency
of IDR, INR, and CHF.

An options for digits is added on the rounding field in the
`account.cash.rounding` list and form view, to make sure the additional
decimal points are shown (it's set to hide anything smaller than 2
digits behind the decimal separator)

In master (18.1), an additional preferred default value for the rounding
field will be saved on the partner of the move, and will be made a
priority over all current `ir.default` for this rounding field.

task-id: 4338116