Implement 'scrollEnabled' prop

Summary:
@public

The content of `WKWebView` renders within a scrollview. In this diff, I'm introducing the prop `scrollEnabled` to allow developers to control whether scrolling is enabled within the scroll view, or not.

Reviewed By: mmmulani

Differential Revision: D6307001

fbshipit-source-id: 5a199c6c3b8535e45a5a3cb6041e822bb7af2362

Author: RSNara

React/Views/RCTWKWebView.h

@@ -20,6 +20,7 @@
 @property (nonatomic, copy) NSDictionary *source;
 @property (nonatomic, assign) BOOL messagingEnabled;
 @property (nonatomic, copy) NSString *injectedJavaScript;
+@property (nonatomic, assign) BOOL scrollEnabled;
 
 - (void)postMessage:(NSString *)message;
 

React/Views/RCTWKWebView.m

@@ -85,6 +85,11 @@ - (void)setSource:(NSDictionary *)source
   }
 }
 
+- (void)setScrollEnabled:(BOOL)scrollEnabled
+{
+  _webView.scrollView.scrollEnabled = scrollEnabled;
+}
+
 - (void)postMessage:(NSString *)message
 {
   NSDictionary *eventInitDict = @{@"data": message};

React/Views/RCTWKWebViewManager.m

@@ -37,5 +37,8 @@ - (UIView *)view
 }
 
 RCT_REMAP_VIEW_PROPERTY(bounces, _webView.scrollView.bounces, BOOL)
+RCT_CUSTOM_VIEW_PROPERTY(scrollEnabled, BOOL, RCTWKWebView) {
+  view.scrollEnabled = json == nil ? true : [RCTConvert BOOL: json];
+}
 
 @end