New port: games/flightgear-terragear

TerraGear is a collection of tools for building scenery for the
FlightGear project. Generally, the process is done in two steps:

1. Preprocess the original raw data. This chops up the data into the FG tiling scheme and saves it in a simple, intermediate format.
2. Collect all the different pieces of intermediate data and assemble them into a 3d model of the terrain.

WWW: https://github.com/FlightGear/terragear

PR: 223648
Submitted by: Michael Danilov <mike.d.ft402@gmail.com>