Adds ExplicitAction class to track argument usage in AppLauncher (#313)

# Description

Introduced a custom argparse action to determine if command-line
arguments were explicitly provided by the user.

* Updated the device argument in AppLauncher to utilize ExplicitAction,
allowing for better handling of device settings based on user input.
* Adjusted device resolution logic to account for explicit device
specification, improving the default behavior when running in XR mode.

Fixes # (issue)

## Type of change

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

## Screenshots

Please attach before and after screenshots of the change if applicable.

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] 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

---------
Co-authored-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: Kelly Guo <kellyguo123@hotmail.com>

source/isaaclab/isaaclab/app/app_launcher.py

@@ -30,6 +30,16 @@ with contextlib.suppress(ModuleNotFoundError):
 from isaacsim import SimulationApp
 
 
+class ExplicitAction(argparse.Action):
+    """Custom action to track if an argument was explicitly passed by the user."""
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        # Set the parameter value
+        setattr(namespace, self.dest, values)
+        # Set a flag indicating the parameter was explicitly passed
+        setattr(namespace, f"{self.dest}_explicit", True)
+
+
 class AppLauncher:
     """A utility class to launch Isaac Sim application based on command-line arguments and environment variables.
 
@@ -277,7 +287,8 @@ class AppLauncher:
         arg_group.add_argument(
             "--device",
             type=str,
-            default=AppLauncher._APPLAUNCHER_CFG_INFO["device"][1] if "--xr" not in sys.argv else None,
+            action=ExplicitAction,
+            default=AppLauncher._APPLAUNCHER_CFG_INFO["device"][1],
             help='The device to run the simulation on. Can be "cpu", "cuda", "cuda:N", where N is the device ID',
         )
         # Add the deprecated cpu flag to raise an error if it is used
@@ -604,10 +615,12 @@ class AppLauncher:
     def _resolve_device_settings(self, launcher_args: dict):
         """Resolve simulation GPU device related settings."""
         self.device_id = 0
-        device = launcher_args.get("device")
-        if device is None:
-            # If no device is specified, default to the GPU device if we are not running in XR
-            device = "cpu" if self._xr else AppLauncher._APPLAUNCHER_CFG_INFO["device"][1]
+        device = launcher_args.get("device", AppLauncher._APPLAUNCHER_CFG_INFO["device"][1])
+
+        device_explicitly_passed = launcher_args.pop("device_explicit", False)
+        if self._xr and not device_explicitly_passed:
+            # If no device is specified, default to the CPU device if we are running in XR
+            device = "cpu"
 
         if "cuda" not in device and "cpu" not in device:
             raise ValueError(