The previous fix restored stock_available but then there was no way to exclude the incomming moves from the count. This belongs in stock_available_immediately, restoring it cleanly.
This commit also takes care to respect the distinction between templates and variants, so it should fix https://github.com/OCA/stock-logistics-warehouse/issues/73 too.
Generic module to compute the stock quantity available to promise using several implementations.
stock_available_immediatly is changed to become the first optional implementation.
Cherry pick of commit 0b060f619f from the v7 branch
