mark init as designated initializer for RCTNetworking (#41252)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41252

Changelog: [Internal]

let's add compile time guarantee that `RCTNetworking` must go thru `initWithDisabledObservation`.

Reviewed By: cipolleschi

Differential Revision: D50764524

fbshipit-source-id: fcc92411b26343bd5977dbfa1b2e95f0841e4ac8

packages/react-native/Libraries/Network/RCTNetworking.h

@@ -28,6 +28,8 @@
 
 @interface RCTNetworking : RCTEventEmitter
 
+- (instancetype)init NS_DESIGNATED_INITIALIZER;
+
 /**
  * Allows RCTNetworking instances to be initialized with handlers.
  * The handlers will be requested via the bridge's moduleForName method when required.

packages/react-native/Libraries/Network/RCTNetworking.mm

@@ -170,7 +170,7 @@ RCT_EXPORT_MODULE()
 - (instancetype)initWithHandlersProvider:
     (NSArray<id<RCTURLRequestHandler>> * (^)(RCTModuleRegistry *moduleRegistry))getHandlers
 {
-  if (self = [super initWithDisabledObservation]) {
+  if (self = [self init]) {
     _handlersProvider = getHandlers;
   }
   return self;