grutil: Add control over heightfield filtering in shaderTerrainMesh
grutil: Add control over heightfield filtering in shaderTerrainMesh

Signed-off-by: deflected <4e8b39f4fad01cf7ba570fbff685e6b412438ff4@users.noreply.github.com>

chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d,chandler14362/panda3d