feat(WKWebView): [ios] Add allowsLinkPreview property to WKWebView (#170)

* [ios] Add ‘allowsLinkPreview’ property to iOS WKWebView.

* Add divider in docs

* Typo: add hyphen -> _allowsLinkPreview

docs/Reference.md

 - [`allowFileAccess`](Reference.md#allowFileAccess)
 - [`saveFormDataDisabled`](Reference.md#saveFormDataDisabled)
 - [`pagingEnabled`](Reference.md#pagingEnabled)
+- [`allowsLinkPreview`](Reference.md#allowsLinkPreview)
 
 ## Methods Index
 
 | ------- | -------- | -------- |
 | boolean | No       | iOS      |
 
+---
+
+### `allowsLinkPreview`
+
+A Boolean value that determines whether pressing on a link displays a preview of the destination for the link. In iOS this property is available on devices that support 3D Touch. In iOS 10 and later, the default value is true; before that, the default value is false.
+
+| Type    | Required | Platform |
+| ------- | -------- | -------- |
+| boolean | No       | iOS      |
+
 ## Methods
 
 ### `extraNativeComponentConfig()`

ios/RNCWKWebView.h

 @property (nonatomic, assign) BOOL hideKeyboardAccessoryView;
 @property (nonatomic, assign) BOOL allowsBackForwardNavigationGestures;
 @property (nonatomic, copy) NSString *userAgent;
+@property (nonatomic, assign) BOOL allowsLinkPreview;
 
 - (void)postMessage:(NSString *)message;
 - (void)injectJavaScript:(NSString *)script;

ios/RNCWKWebView.m

     _webView.scrollView.scrollEnabled = _scrollEnabled;
     _webView.scrollView.pagingEnabled = _pagingEnabled;
     _webView.scrollView.bounces = _bounces;
+    _webView.allowsLinkPreview = _allowsLinkPreview;
     [_webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:nil];
     _webView.allowsBackForwardNavigationGestures = _allowsBackForwardNavigationGestures;
+
     if (_userAgent) {
       _webView.customUserAgent = _userAgent;
     }

ios/RNCWKWebViewManager.m

 RCT_EXPORT_VIEW_PROPERTY(allowsBackForwardNavigationGestures, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(pagingEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(userAgent, NSString)
+RCT_EXPORT_VIEW_PROPERTY(allowsLinkPreview, BOOL)
 
 /**
  * Expose methods to enable messaging the webview.

js/WebView.ios.js

           this.props.mediaPlaybackRequiresUserAction
         }
         dataDetectorTypes={this.props.dataDetectorTypes}
+        allowsLinkPreview={this.props.allowsLinkPreview}
         {...nativeConfig.props}
       />
     );

js/WebViewTypes.js

    * The custom user agent string.
    */
   userAgent?: ?string,
+
+  /**
+   * A Boolean value that determines whether pressing on a link
+   * displays a preview of the destination for the link.
+   *
+   * This property is available on devices that support 3D Touch.
+   * In iOS 10 and later, the default value is `true`; before that, the default value is `false`.
+   * @platform ios
+   */
+  allowsLinkPreview?: ?boolean,
 |}>;
 
 export type AndroidWebViewProps = $ReadOnly<{|

typings/index.d.ts

   /**
    * If true, this will be able horizontal swipe gestures when using the WKWebView. The default value is `false`.
    */
-  allowsBackForwardNavigationGestures?: boolean
+  allowsBackForwardNavigationGestures?: boolean;
+
+  /**
+   * A Boolean value that determines whether pressing on a link
+   * displays a preview of the destination for the link.
+   *
+   * This property is available on devices that support 3D Touch.
+   * In iOS 10 and later, the default value is `true`; before that, the default value is `false`.
+   * @platform ios
+   */
+  allowsLinkPreview?: boolean;
 }
 
 export interface AndroidWebViewProps {