MLKitAnalyser should use cameraExecutor instead of main executor

[renebaeu]

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? ->