[ReactNative] Proxy bundleURL on RCTBatchedBridge

Summary:
Fixes #2126

`RCTBatchedBridge` didn't implement `bundleURL`, that was available on the public
bridge interface, so it'd always be `nil`, and setting it would just be ignored.

React/Base/RCTBatchedBridge.m

@@ -146,6 +146,16 @@ RCT_NOT_IMPLEMENTED(-initWithBundleURL:(__unused NSURL *)bundleURL
   _parentBridge.executorClass = executorClass;
 }
 
+- (NSURL *)bundleURL
+{
+  return _parentBridge.bundleURL;
+}
+
+- (void)setBundleURL:(NSURL *)bundleURL
+{
+  _parentBridge.bundleURL = bundleURL;
+}
+
 - (BOOL)isLoading
 {
   return _loading;

React/Base/RCTBridge.h

@@ -93,7 +93,7 @@ RCT_EXTERN NSString *RCTBridgeModuleNameForClass(Class bridgeModuleClass);
 /**
  * URL of the script that was loaded into the bridge.
  */
-@property (nonatomic, copy) NSURL *bundleURL;
+@property (nonatomic, strong) NSURL *bundleURL;
 
 @property (nonatomic, strong) Class executorClass;