fix: Fix view-not-found race condition in C++ code (#511)

* Add custom `onViewReady` event to get layout

`componentDidMount` is async, so the native view _might_ not exist yet causing a race condition in the `setFrameProcessor` code.

This PR fixes this by calling `setFrameProcessor` only after the native view has actually mounted, and to ensure that I created a custom event that fires at that point.

* Update CameraView.swift

android/src/main/java/com/mrousavy/camera/CameraView+Events.kt

@@ -42,6 +42,12 @@ fun CameraView.invokeOnFrameProcessorPerformanceSuggestionAvailable(currentFps:
   reactContext.getJSModule(RCTEventEmitter::class.java).receiveEvent(id, "cameraPerformanceSuggestionAvailable", event)
 }
 
+fun CameraView.invokeOnViewReady() {
+  val event = Arguments.createMap()
+  val reactContext = context as ReactContext
+  reactContext.getJSModule(RCTEventEmitter::class.java).receiveEvent(id, "cameraViewReady", event)
+}
+
 private fun errorToMap(error: Throwable): WritableMap {
   val map = Arguments.createMap()
   map.putString("message", error.message)

android/src/main/java/com/mrousavy/camera/CameraView.kt

@@ -108,6 +108,7 @@ class CameraView(context: Context, private val frameProcessorThread: ExecutorSer
     }
 
   // private properties
+  private var isMounted = false
   private val reactContext: ReactContext
     get() = context as ReactContext
 
@@ -266,6 +267,10 @@ class CameraView(context: Context, private val frameProcessorThread: ExecutorSer
   override fun onAttachedToWindow() {
     super.onAttachedToWindow()
     updateLifecycleState()
+    if (!isMounted) {
+      isMounted = true
+      invokeOnViewReady()
+    }
   }
 
   override fun onDetachedFromWindow() {

android/src/main/java/com/mrousavy/camera/CameraViewManager.kt

@@ -55,6 +55,7 @@ class CameraViewManager(reactContext: ReactApplicationContext) : SimpleViewManag
 
   override fun getExportedCustomDirectEventTypeConstants(): MutableMap<String, Any>? {
     return MapBuilder.builder<String, Any>()
+      .put("cameraViewReady", MapBuilder.of("registrationName", "onViewReady"))
       .put("cameraInitialized", MapBuilder.of("registrationName", "onInitialized"))
       .put("cameraError", MapBuilder.of("registrationName", "onError"))
       .put("cameraPerformanceSuggestionAvailable", MapBuilder.of("registrationName", "onFrameProcessorPerformanceSuggestionAvailable"))