Updates sensor data always if visualization enabled

# Description

This MR ensures that the sensor buffers are always updated in
visualization mode. Otherwise, the sensors are not visualizable without
someone accessing the `data` property.

## Type of change

- New feature (non-breaking change which adds functionality)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [x] 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
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

source/extensions/omni.isaac.orbit/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.9.50"
+version = "0.9.51"
 
 # Description
 title = "ORBIT framework for Robot Learning"

source/extensions/omni.isaac.orbit/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.9.51 (2023-11-29)
+~~~~~~~~~~~~~~~~~~~
+
+Changed
+^^^^^^^
+
+* Changed the :meth:`omni.isaac.orbit.sensor.SensorBase.update` method to always recompute the buffers if
+  the sensor is in visualization mode.
+
+Added
+^^^^^
+
+* Added available entities to the error message when accessing a non-existent entity in the
+  :class:`InteractiveScene` class.
+* Added a warning message when the user tries to reference an invalid prim in the :class:`FrameTransformer` sensor.
+
+
 0.9.50 (2023-11-28)
 ~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.orbit/omni/isaac/orbit/scene/interactive_scene.py

@@ -306,14 +306,17 @@ class InteractiveScene:
         # check if it is a terrain
         if key == "terrain":
             return self.terrain
+
+        all_keys = ["terrain"]
         # check if it is in other dictionaries
         for asset_family in [self.articulations, self.rigid_objects, self.sensors, self.extras]:
             out = asset_family.get(key)
             # if found, return
             if out is not None:
                 return out
+            all_keys += list(asset_family.keys())
         # if not found, raise error
-        raise KeyError(f"Scene entity with key '{key}' not found.")
+        raise KeyError(f"Scene entity with key '{key}' not found. Available Entities: '{all_keys}'")
 
     """
     Internal methods.

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sensors/frame_transformer/frame_transformer.py

@@ -151,7 +151,13 @@ class FrameTransformer(SensorBase):
         frame_offsets = [None] + [target_frame.offset for target_frame in self.cfg.target_frames]
         for frame, prim_path, offset in zip(frames, frame_prim_paths, frame_offsets):
             # Find correct prim
-            for matching_prim_path in prim_utils.find_matching_prim_paths(prim_path):
+            matching_prims = prim_utils.find_matching_prim_paths(prim_path)
+            if len(matching_prims) == 0:
+                raise ValueError(
+                    f"Failed to create frame transformer for frame '{frame}' with path '{prim_path}'."
+                    " No matching prims were found."
+                )
+            for matching_prim_path in matching_prims:
                 prim = prim_utils.get_prim_at_path(matching_prim_path)
                 # check if it is a rigid prim
                 if not prim.HasAPI(UsdPhysics.RigidBodyAPI):

source/extensions/omni.isaac.orbit/omni/isaac/orbit/sensors/sensor_base.py

@@ -51,6 +51,8 @@ class SensorBase(ABC):
         self.cfg = cfg
         # flag for whether the sensor is initialized
         self._is_initialized = False
+        # flag for whether the sensor is in visualization mode
+        self._is_visualizing = False
 
         # note: Use weakref on callbacks to ensure that this object can be deleted when its destructor is called.
         # add callbacks for stage play/stop
@@ -140,6 +142,8 @@ class SensorBase(ABC):
             return False
         # toggle debug visualization objects
         self._set_debug_vis_impl(debug_vis)
+        # toggle debug visualization flag
+        self._is_visualizing = debug_vis
         # toggle debug visualization handles
         if debug_vis:
             # create a subscriber for the post update event if it doesn't exist
@@ -178,7 +182,7 @@ class SensorBase(ABC):
         # Update the buffers
         # TODO (from @mayank): Why is there a history length here when it doesn't mean anything in the sensor base?!?
         #   It is only for the contact sensor but there we should redefine the update function IMO.
-        if force_recompute or (self.cfg.history_length > 0):
+        if force_recompute or self._is_visualizing or (self.cfg.history_length > 0):
             self._update_outdated_buffers()
 
     """