MLKitAnalyser should use cameraExecutor instead of main executor

https://github.com/android/camera-samples/blob/f284e1d9c740fbe0db27ae41b07a7bbc01361499/CameraX-MLKit/app/src/main/java/com/example/camerax_mlkit/MainActivity.kt#L71

```
cameraController.setImageAnalysisAnalyzer(
ContextCompat.getMainExecutor(this), // <- cameraExecutor
MlKitAnalyzer(
listOf(barcodeScanner),
COORDINATE_SYSTEM_VIEW_REFERENCED,
ContextCompat.getMainExecutor(this)
) { result: MlKitAnalyzer.Result? ->
```

Open CameraX-MLKit/app/src/main/java/com/example/camerax_mlkit/MainActivity.kt around line 71 and inspect how cameraExecutor is defined and passed to the analyzer setup. Confirm the intended executor arguments, then verify that the CameraX-MLKit sample still builds and uses cameraExecutor for the requested analysis work.

Written by the indexing model from the issue text.