Fixes errors in tools and tutorial scripts (isaac-sim#1669)

# Description

A few scripts in the tools and tutorials folder had outdated APIs that
caused errors when run.
This scripts fixes issues with 2 scripts:

- check_instanceable.py used an old `enable_flatcache` API that no
longer exists. this has been replaced with the new `enable_fabric` API
- run_usd_camera.py was indexing camera data outputs with incorrect
keys/indices, which is now fixed

## Type of change

<!-- As you go through the list, delete the ones that are not
applicable. -->

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

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.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
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
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putting an x character in it

For example,
- [x] I have done this task
- [ ] I have not done this task
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source/standalone/tools/check_instanceable.py

@@ -82,12 +82,12 @@ def main():
     sim = SimulationContext(
         stage_units_in_meters=1.0, physics_dt=0.01, rendering_dt=0.01, backend="torch", device="cuda:0"
     )
-    # enable flatcache which avoids passing data over to USD structure
+    # enable fabric which avoids passing data over to USD structure
     # this speeds up the read-write operation of GPU buffers
     if sim.get_physics_context().use_gpu_pipeline:
-        sim.get_physics_context().enable_flatcache(True)
+        sim.get_physics_context().enable_fabric(True)
     # enable hydra scene-graph instancing
-    # this is needed to visualize the scene when flatcache is enabled
+    # this is needed to visualize the scene when fabric is enabled
     set_carb_setting(sim._settings, "/persistent/omnihydra/useSceneGraphInstancing", True)
 
     # Create interface to clone the scene

source/standalone/tutorials/04_sensors/run_usd_camera.py

@@ -252,7 +252,7 @@ def run_simulator(sim: sim_utils.SimulationContext, scene_entities: dict):
             # Derive pointcloud from camera at camera_index
             pointcloud = create_pointcloud_from_depth(
                 intrinsic_matrix=camera.data.intrinsic_matrices[camera_index],
-                depth=camera.data.output[camera_index]["distance_to_image_plane"],
+                depth=camera.data.output["distance_to_image_plane"][camera_index],
                 position=camera.data.pos_w[camera_index],
                 orientation=camera.data.quat_w_ros[camera_index],
                 device=sim.device,