Request: Terrain Following Visualization

We need a profile view to visualize the terrain and how the autopilot will respond to it while utilizing Terrain Following. The Elevation Graph does not show the aircraft following the terrain. There are two important aspects to flight planning with TF that are missing:
1. How will the autopilot fly the terrain utilizing the TERRAIN_LOOKAHD parameter? I'm envisioning a profile view with a TERRAIN_LOOKAHD slider that changes the smoothing effect that the autopilot will have over the varying terrain. The algorithm used in the autopilot would need to be duplicated in MP to show how it would intend to fly the altitudes.
2. What are the gradients that my plane will be expected to fly? The flight plan gradients are a critical part of flight planning decsion making, but they no longer work if utilizing TF. Either with '#1 above, or listed separately in a new WP column, we need to be able to see if the flight plan gradients are reasonable.

We also need a clear way to see if TF is active or not. Perhaps a HUD flag that says "Terrain Following" so the pilot doesn't get confused over the behavior of the aircraft.

No files, tests, or entry points are named in the issue. Start by scoping the existing Elevation Graph, terrain-following behavior, flight-plan gradient display, and HUD; the work is done when the profile view, TERRAIN_LOOKAHD control, gradient information, and clear Terrain Following status are defined and implemented.

Written by the indexing model from the issue text.