Considering recent recurring bug reports and the fact that bridge modules
now automatically compute the cost considering logistics, timesheets & expense
flows, the ability to manually edit the cost on a sale.order.line is now disabled.
In most cases, manually specified costs are automatically reset because of
stock/timesheets/expenses added dependencies on the purchase_price field.
Also adapt existing tests and use the new Sale tests common.
closesodoo/odoo#97977
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>