Easing functions are not exposed

[mihe]

For whatever reason the easing functions in UKismetMathLibrary were marked as BlueprintInternalUseOnly and instead dynamically chosen through the custom Blueprint node UK2Node_EaseFunction. This has the unfortunate consequence of the easing functions not being exposed in the typings.

Either we give those functions special treatment and let them get exposed despite being BlueprintInternalUseOnly, or we add something like TsuMathLibrary. Alternatively if #3 gets solved they could get added as extensions to UKismetMathLibrary.