feat(iOS): added `contentInsetAdjustmentBehavior` prop

* Adding a `contentInsetAdjustmentBehavior` prop to the WebView for iOS.
This controls the way iOS will automatically adjust the insets when the
webview is behind things like the iPhone X notch.

* Removing the code to explicitly pass contentInsetAdjustmentBehavior to the WebView since it is already passed in otherProps.

docs/Reference.md

 - [`bounces`](Reference.md#bounces)
 - [`overScrollMode`](Reference.md#overscrollmode)
 - [`contentInset`](Reference.md#contentinset)
+- [`contentInsetAdjustmentBehavior`](Reference.md#contentInsetAdjustmentBehavior)
 - [`dataDetectorTypes`](Reference.md#datadetectortypes)
 - [`scrollEnabled`](Reference.md#scrollenabled)
 - [`directionalLockEnabled`](Reference.md#directionalLockEnabled)
 
 ---
 
+### `contentInsetAdjustmentBehavior`
+
+This property specifies how the safe area insets are used to modify the content area of the scroll view. The default value of this property is "never". Available on iOS 11 and later. Defaults to `never`.
+
+Possible values:
+
+- `automatic`
+- `scrollableAxes`
+- `never`
+- `always`
+
+| Type   | Required | Platform |
+| ------ | -------- | -------- |
+| string | No       | iOS      |
+
+---
+
 ### `dataDetectorTypes`
 
 Determines the types of data converted to clickable URLs in the web view's content. By default only phone numbers are detected.

ios/RNCWKWebView.m

   BOOL _isFullScreenVideoOpen;
   UIStatusBarStyle _savedStatusBarStyle;
   BOOL _savedStatusBarHidden;
+
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 /* __IPHONE_11_0 */
+  UIScrollViewContentInsetAdjustmentBehavior _savedContentInsetAdjustmentBehavior;
+#endif
 }
 
 - (instancetype)initWithFrame:(CGRect)frame
     _savedKeyboardDisplayRequiresUserAction = YES;
     _savedStatusBarStyle = RCTSharedApplication().statusBarStyle;
     _savedStatusBarHidden = RCTSharedApplication().statusBarHidden;
+
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 /* __IPHONE_11_0 */
+    _savedContentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+#endif
   }
 
   if (@available(iOS 12.0, *)) {
     }
 #if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 /* __IPHONE_11_0 */
     if ([_webView.scrollView respondsToSelector:@selector(setContentInsetAdjustmentBehavior:)]) {
-      _webView.scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
+      _webView.scrollView.contentInsetAdjustmentBehavior = _savedContentInsetAdjustmentBehavior;
     }
 #endif
 
   _webView.backgroundColor = backgroundColor;
 }
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 /* __IPHONE_11_0 */
+- (void)setContentInsetAdjustmentBehavior:(UIScrollViewContentInsetAdjustmentBehavior)behavior
+{
+    _savedContentInsetAdjustmentBehavior = behavior;
+    if (_webView == nil) {
+        return;
+    }
+
+    if ([_webView.scrollView respondsToSelector:@selector(setContentInsetAdjustmentBehavior:)]) {
+        CGPoint contentOffset = _webView.scrollView.contentOffset;
+        _webView.scrollView.contentInsetAdjustmentBehavior = behavior;
+        _webView.scrollView.contentOffset = contentOffset;
+    }
+}
+#endif
+
 /**
  * This method is called whenever JavaScript running within the web view calls:
  *   - window.webkit.messageHandlers[MessageHandlerName].postMessage

ios/RNCWKWebViewManager.m

 @interface RNCWKWebViewManager () <RNCWKWebViewDelegate>
 @end
 
+@implementation RCTConvert (UIScrollView)
+
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 /* __IPHONE_11_0 */
+RCT_ENUM_CONVERTER(UIScrollViewContentInsetAdjustmentBehavior, (@{
+                                                                  @"automatic": @(UIScrollViewContentInsetAdjustmentAutomatic),
+                                                                  @"scrollableAxes": @(UIScrollViewContentInsetAdjustmentScrollableAxes),
+                                                                  @"never": @(UIScrollViewContentInsetAdjustmentNever),
+                                                                  @"always": @(UIScrollViewContentInsetAdjustmentAlways),
+                                                                  }), UIScrollViewContentInsetAdjustmentNever, integerValue)
+#endif
+
+@end
+
 @implementation RNCWKWebViewManager
 {
   NSConditionLock *_shouldStartLoadLock;
 RCT_EXPORT_VIEW_PROPERTY(cacheEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(allowsLinkPreview, BOOL)
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 /* __IPHONE_11_0 */
+RCT_EXPORT_VIEW_PROPERTY(contentInsetAdjustmentBehavior, UIScrollViewContentInsetAdjustmentBehavior)
+#endif
+
 /**
  * Expose methods to enable messaging the webview.
  */

src/WebViewTypes.ts

   automaticallyAdjustContentInsets?: boolean;
   bounces?: boolean;
   contentInset?: ContentInsetProp;
+  contentInsetAdjustmentBehavior?: 'automatic'| 'scrollableAxes' | 'never' | 'always';
   dataDetectorTypes?: DataDetectorTypes | ReadonlyArray<DataDetectorTypes>;
   decelerationRate?: number;
   directionalLockEnabled?: boolean;
    */
   automaticallyAdjustContentInsets?: boolean;
 
+  /**
+   * This property specifies how the safe area insets are used to modify the
+   * content area of the scroll view. The default value of this property is
+   * "never". Available on iOS 11 and later.
+   */
+  contentInsetAdjustmentBehavior?: 'automatic'| 'scrollableAxes' | 'never' | 'always'
+
   /**
    * The amount by which the web view content is inset from the edges of
    * the scroll view. Defaults to {top: 0, left: 0, bottom: 0, right: 0}.