[VISUAL] Add an Input to control MaxDensityLerp on the env_fog_controller. (Akin to L4D's input.)

[12gaugez]

Is your feature request related to a problem? Please describe.

I'm creating a map, and i have been messing around with the fog settings via I/Os on a trigger. Ever since EP1, StartFogTransition has been implemented, and all lerp inputs work through this. However, there doesn't seem to be an option in Mapbase that directly does this for the fog's density. Ever since L4D, this lerp option has existed, but here it doesn't seem to exist. Heck, even the VDC lists the SetMaxDensity Input as (may be) missing in most FGDs.

Describe the solution you'd like

The SetMaxDensityLerpTo input to be either re-created/directly ported into Mapbase, and to have a smooth transition of the density of fog via inputs and outputs.

Describe alternatives you've considered

I've considered using the SetStartDist and SetEndDist inputs, but i'm not too sure on how this will affect things.

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Additional context

Should this feature of some sort already be in Mapbase, simply disregard my request.