Resource scale computation optimizations

When we're in a non fractional-scaling context or when fractional scaling is enabled but we've one single monitor or multiple monitors with similar DPIs (so that the applied scaling is ceilied to a common integer) we can avoid all the actor resource scale computation and instead use a global resource scale value.

At the current state, in fact, to achieve better visual quality we ceil the resource scale values to the closest integer, and this allows us to apply an optimization to multiple scenarios.

Basically in case all the stage views share the same ceilied scaling value, we can assume that we're painting all the actors with the same resource scale, and thus avoid the computation, unless we don't need the real scaling. In such case we just do what we've been doning so far.

But in general, in the most common scenarios, this should reduce a lot the resource scale computation.