Allow using a custom loading view

Author: mars-lan

ios/RCTSplashScreen/RCTSplashScreen/RCTSplashScreen.h

@@ -11,5 +11,6 @@ typedef NS_ENUM(NSInteger, RCTCameraAspect) {
 
 + (void)open:(RCTRootView *)v;
 + (void)open:(RCTRootView *)v withImageNamed:(NSString *)imgName;
++ (void)open:(RCTRootView *)v withLoadingView:(UIView *)loadingView;
 
 @end

ios/RCTSplashScreen/RCTSplashScreen/RCTSplashScreen.m

@@ -30,6 +30,14 @@ + (void)open:(RCTRootView *)v withImageNamed:(NSString *)imageName {
     [rootView setLoadingView:view];
 }
 
++ (void)open:(RCTRootView *)v withLoadingView:(UIView *)loadingView {
+  rootView = v;
+
+  [[NSNotificationCenter defaultCenter] removeObserver:rootView  name:RCTContentDidAppearNotification object:rootView];
+
+  [rootView setLoadingView:loadingView];
+}
+
 RCT_EXPORT_METHOD(close:(NSDictionary *)options) {
     if (!rootView) {
         return;