[FIX] sale,purchase: do not enforce company at _prepare_* level.

By specifying the with_company at a higher level:
1) The risk of multi-company conflicts decreases
2) We allow customizations to use _prepare_* methods to potentially
create records in other companies when needed.

closes odoo/odoo#55192

X-original-commit: 33c767e1778d2b1fc83aaaea92c3c2aa008b9520
Related: odoo/enterprise#12105
Signed-off-by: Toufik Benjaa (tbe) <tbe@odoo.com>
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>