When IsTraitDisabled is set, ModifyRender doesn't actually alter the sequence, so we can just return it directly and avoid adding another layer of enumerable. If it is unset, then the modifying enumerable has one less condition to check inside the loop.
Upgradeable traits are notified whenever an upgrade of their declared types are granted or revoked. The traits maintain their own internal level counter, which is then used to enable or disable the trait functionality. A trait can register for multiple upgrade types which then all affect the internal level counter.
IDisabledTrait for identifying (and filtering) disabled traits
UpgradableTrait provides an abstract base for traits to support upgrade levels
Added IDisabledTrait support to GlobalButtonOrderGenerator
Includes rework by pchote with alterations.
