feat: add torch plugin for iOS and Android (#3551)

* feat(barcode-scanner): add torch toggle

* feat: torch plugin

* fix

---------

Co-authored-by: Lucas Nogueira <lucas@tauri.app>

plugins/barcode-scanner/android/src/main/java/BarcodeScannerPlugin.kt

@@ -75,6 +75,10 @@ class BarcodeScannerPlugin(private val activity: Activity) : Plugin(activity),
     private var cameraProvider: ProcessCameraProvider? = null
     private var graphicOverlay: GraphicOverlay? = null
     private var camera: Camera? = null
+        set(value) {
+            field = value
+            activeCamera = value
+        }
     private var vibrator: Vibrator? = null
 
     private var scannerOptions: BarcodeScannerOptions? = null
@@ -416,4 +420,19 @@ class BarcodeScannerPlugin(private val activity: Activity) : Plugin(activity),
     private fun openSettingsResult(invoke: Invoke, result: ActivityResult) {
         invoke.resolve()
     }
+
+    companion object {
+        @Volatile
+        private var activeCamera: Camera? = null
+
+        /**
+         * The camera bound by an active scan, or `null` when no scan is running.
+         *
+         * Looked up through reflection by the torch plugin (`app.tauri.torch`): while a scan holds the
+         * camera, Android rejects `CameraManager.setTorchMode`, so the flash must be driven through
+         * this camera's `CameraControl` instead. Keep the name and signature stable.
+         */
+        @JvmStatic
+        fun getActiveCamera(): Camera? = activeCamera
+    }
 }