This allows custom movement generators to set ad-hoc properties on
generated movements depending on properties of the corresponding
input movement.

There was already _getUpdatePropertyDict which is similar, but was
sometimes not enough because it can only be use to set extra
properties on all movements.

As a result, when we needed a rule with custom properties on
generated movements, we resorted to overriding getGeneratedMovementList
and duplicating the full logic of the method. Existing cases have
been updated to use the new _updateGeneratedMovementList and in the
case of InventoryAssetPriceAccountingRuleMovementGenerator we no
longer need to duplicate the logic.

Also remove the comment suggesting overriding getGeneratedMovementList
in subclasses, now several "extension" methods exists, so it should
not be needed to override getGeneratedMovementList, every needs
should be coverred by defining _updateGeneratedMovementList or
_getUpdatePropertyDict