Refactored subview management

Summary:
This diff refactors the view update process into two stages:

1. The `reactSubviews` array is set, whose order matches the order of the JS components and shadowView components, as specified by the UIManager.
2. The `didUpdateReactSubviews` method is called, which actually inserts the reactSubviews into the view hierarchy.

This simplifies a lot of the hacks we had for special-case treatment of subviews: In many cases we don't want to actually insert `reactSubviews` into the parentView, and we had a bunch of component-specific solutions for that (typically overriding all of the reactSubviews methods to store views in an array). Now, we can simply override the `didUpdateReactSubviews` method for those views to do nothing, or do something different.

Reviewed By: wwjholmes

Differential Revision: D3396594

fbshipit-source-id: 92fc56fd31db0cfc66aac3d1634a4d4ae3903085

React/Views/RCTMap.m

@@ -23,7 +23,6 @@ const CGFloat RCTMapZoomBoundBuffer = 0.01;
 {
   UIView *_legalLabel;
   CLLocationManager *_locationManager;
-  NSMutableArray<UIView *> *_reactSubviews;
 }
 
 - (instancetype)init
@@ -31,7 +30,6 @@ const CGFloat RCTMapZoomBoundBuffer = 0.01;
   if ((self = [super init])) {
 
     _hasStartedRendering = NO;
-    _reactSubviews = [NSMutableArray new];
 
     // Find Apple link label
     for (UIView *subview in self.subviews) {
@@ -51,19 +49,9 @@ const CGFloat RCTMapZoomBoundBuffer = 0.01;
   [_regionChangeObserveTimer invalidate];
 }
 
-- (void)insertReactSubview:(UIView *)subview atIndex:(NSInteger)atIndex
+- (void)reactUpdateSubviews
 {
-  [_reactSubviews insertObject:subview atIndex:atIndex];
-}
-
-- (void)removeReactSubview:(UIView *)subview
-{
-  [_reactSubviews removeObject:subview];
-}
-
-- (NSArray<UIView *> *)reactSubviews
-{
-  return _reactSubviews;
+  // Do nothing, as annotation views are managed by `setAnnotations:` method
 }
 
 - (void)layoutSubviews