Fixes using strings for shapes in `MeshRepeatedObjectsTerrainCfg` (#213)

# Description

Meshes such as "box", "cylinder" and "cone" are defined in
`omni.isaac.orbit.terrains.trimesh.utils.py` and can be used in configs
such as
[here](https://github.com/isaac-orbit/orbit/blob/17fc724de7386c919f6f0367980c1d8e9855c446/extensions/omni.isaac.orbit/omni/isaac/orbit/terrains/trimesh/mesh_terrains_cfg.py#L187).
In the example, their definition as a string is allowed but as they are
not explicitly imported, the general statement cannot capture the
missing functions. This PR makes sure that all mesh helper functions in
`utils.py` are imported and that the string format can be used.

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file

source/extensions/omni.isaac.orbit/omni/isaac/orbit/terrains/trimesh/mesh_terrains.py

@@ -13,6 +13,7 @@ import torch
 import trimesh
 from typing import TYPE_CHECKING
 
+from .utils import *  # noqa: F401, F403
 from .utils import make_border, make_plane
 
 if TYPE_CHECKING:

source/extensions/omni.isaac.orbit/test/terrains/check_mesh_subterrains.py

@@ -329,7 +329,7 @@ def test_star_terrain(difficulty: float):
         trimesh.viewer.SceneViewer(scene=scene, caption="Star Terrain")
 
 
-def test_repeated_objects_terrain(difficulty: float, object_type: str):
+def test_repeated_objects_terrain(difficulty: float, object_type: str, provide_as_string: bool = False):
     # parameters for the terrain
     if object_type == "pyramid":
         cfg = mesh_gen.MeshRepeatedPyramidsTerrainCfg(
@@ -369,6 +369,11 @@ def test_repeated_objects_terrain(difficulty: float, object_type: str):
         )
     else:
         raise ValueError(f"Invalid object type for repeated objects terrain: {object_type}")
+
+    # provide object_type as string (check that the import works)
+    if provide_as_string:
+        cfg.object_type = object_type
+
     # generate the terrain
     meshes, origin = cfg.function(difficulty=difficulty, cfg=cfg)
     # add colors to the meshes based on the height
@@ -419,6 +424,7 @@ if __name__ == "__main__":
     test_repeated_objects_terrain(difficulty=0.75, object_type="pyramid")
     test_repeated_objects_terrain(difficulty=0.75, object_type="cylinder")
     test_repeated_objects_terrain(difficulty=0.75, object_type="box")
+    test_repeated_objects_terrain(difficulty=0.75, object_type="cylinder", provide_as_string=True)
 
     # close the app
     simulation_app.close()