Investigate feasibility for Eye-Dome Lighting in non-perspective views

[DStradley]

Is your feature request related to a problem? Please describe.
In the initial implementation of EDL it was determined that it did not function properly in non-perspective views, so it was disabled there. It did not look promising that it could be made to work, but it is worth further investigation.

Describe the solution you'd like
Ideally, a solution could be found to allow EDL in orthographic views.

Describe alternatives you've considered
Disabling Eye-Dome Lighting in non-perspective views is the current approach.

Additional context
Due to the nature of EDL, we added an auto adjusting term to the Strength setting, which turned out to need 3 different factors to compensate for - cloud size versus current view size, zoom in/out of view, and window size. Without compensation, all of these factors could produce different strength results of the image, making it a lot less usable.
When the same type of factors were applied in ortho views, they did not function well enough. Testing several models showed that some would not even show an EDL effect within the normal range of the DTA controls. Ortho zoom simulates perspective zoom by changing the range of the view frustum (box). So the only things changing are left/right (and top/bottom). We can calculate the size of a pixel in view coordinates, but do not have anything to "normalize" that against for different models. We tried using (far - near), but that did not work well enough. We are not sure that there is a solution for this.