UserPositionDebt.applyPremiumDelta function only uses part of the PremiumDelta struct passed as input parameter

[miguelmtzinf]

This suggestion comes from @StErMi.

When doing changes in the premium, the function UserPositionDebt.getPremiumDelta is used to calculate the current premium data to apply. The restored amount is kept in a separated raw value (e.g. restoredPremiumRay) because it's later passed to the Hub, but this value is already included in offsetRayDelta.

• It's a bit confusing the whole struct is passed userPosition.applyPremiumDelta but restoredPremiumRay value is never used because it has been already included in the premiumDelta.offsetRayDelta.
• UserPositionDebt.getPremiumDelta it's not only a getter but fetches the delta and apply changes from restoredPremiumRay.

We can consider:

1. rename getPremiumDelta to calculatePremiumDelta
2. modify input parameters of applyPremiumDelta so it only takes what's needed.