Replace private bridge categories with private header

Summary:
public

A lot of the core modules have to use private methods in the bridge, specially
since the `RCTBatchedBridge` interface is never exposed. That was leading to a
lot of different private bridge categories spread across different modules,
which makes harder to identify which modules are affected by private API changes.

Replace all the categories with a single private header.

Reviewed By: nicklockwood

Differential Revision: D2757564

fb-gh-sync-id: 793158b9082d542b74a6094ed0db4d5dc3a88f78

React/Base/RCTRootView.m

@@ -14,7 +14,7 @@
 #import <objc/runtime.h>
 
 #import "RCTAssert.h"
-#import "RCTBridge.h"
+#import "RCTBridge+Private.h"
 #import "RCTEventDispatcher.h"
 #import "RCTKeyCommands.h"
 #import "RCTLog.h"
@@ -28,12 +28,6 @@
 
 NSString *const RCTContentDidAppearNotification = @"RCTContentDidAppearNotification";
 
-@interface RCTBridge (RCTRootView)
-
-@property (nonatomic, weak, readonly) RCTBridge *batchedBridge;
-
-@end
-
 @interface RCTUIManager (RCTRootView)
 
 - (NSNumber *)allocateRootTag;