[IMP] mrp(_account): include byproduct cost share in BoM/MO

For improved cost analysis, byproducts can now have a "cost share" (out
of 100%) indicated. This cost share will by multiplied by the total BoM
cost (i.e. components + operations costs) and reflected in the stock
valuation. The final product will also have the byproducts cost
subtracted from its final stock valuation. This is of course only
applies when costing methods are appropriate (i.e. non-standard price).

Additionally, we can now "Compute Price from BoM" for byproducts (via
its product form) and the BoMs that it is a byproduct of are now counted
towards its # BoMs smart button (we will now also see these BoMs when
clicking on the smart button). Of course when there is no cost share for
byproducts then clicking on "Compute Price for BoM" will not change the
a byproduct's cost and if there are multiple BoMs the prodcut is a
byproduct of, the calculation will only be based on the first BoM it
finds (i.e. same as current logic for manufactured products).

BoM Cost report has been updated to include byproducts with cost shares
(byproducts with cost share = 0 will not show up in report).
Additionally we update the report to display operations only costs now
that BoMs are allowed to have no components in them.

Part 1 of Task: 2440068
Upgrade PR: odoo/upgrade#2727
Related ENT PR: odoo/enterprise#20169

Part-of: odoo/odoo#74951