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)