[FIX] account: tax computation on move

- Create the following invoice:
  Line 1: price 0.50, tax 15 %, analytic account set
  Line 2: price 0.10, tax 15 %, analytic account set
- Validate
- Go to the journal entry, cancel it
- Edit the entry, remove an analytic account

The tax line is recomputed from 0.10 to 0.09.

This is because the onchange performs the tax computation on all grouped
lines at once, which is equivalent to a 'round globally' configuration.

We need to split the logic depending on the tax calculation rounding
method.

opw-2117398

closes odoo/odoo#39960

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>