The FCVSnapshot::isUpgradingOrDowngrading currently reports if the FCV is the kUpgrading/kDowngrading transitional FCVs.

Under the old model of setFCV, all setFCV work had to happen in those transitional FCVs.

However in Symmetric FCV, the kUpgrading/kDowngrading FCVs are a barrier to avoid interactions across incompatible features, but setFCV work can happen outside them (in the upgraded/downgraded FCVs).

We should review the existing usages and see if they need to be adapted or we need to change this API.