Request: HUD display of next WP altitude

When flying a complex flight plan in mountainous terrain it would be very useful to have quick reference to the altitude at the next waypoint. I realize there is no mavlink message for this, so it would have to come from the flight plan in MP. Ideally this would appear directly above or below the moving altitude tape, depending on whether the next altitude is above or below current altitude. This is different than the green bar that shows momentary target altitude

No files, tests, or entry points are named. Start by locating the moving altitude tape and the flight-plan waypoint data in Mission Planner; done means the next waypoint altitude appears above or below the tape according to its relation to current altitude and is distinct from the green momentary target-altitude bar.

Written by the indexing model from the issue text.