Add rcMedianFilterWalkableArea() to mmaps generation process to simplify some ground/water areas (cherry picked from commit 7ddbc18aafe61434971013ed6126f5666011ab43)
Add rcMedianFilterWalkableArea() to mmaps generation process to simplify some ground/water areas (cherry picked from commit 7ddbc18aafe61434971013ed6126f5666011ab43)