Implement onPress for Virtual Text nodes

Summary:
When text nodes are nested, as below, `onPress` handlers need to be correctly invoked:
```
render() {
  return (
    <Text onPress={() => console.warn('hi')}>
      hi
      <Text onPress={() => console.warn('ramanpreet')}>ramanpreet</Text>
    </Text>
  );
}
```

In the above example, clicking on "hi" should warn "hi", and clicking on "ramanpreet" should warn "ramanpreet". This diff implements that behaviour.

Reviewed By: shergin

Differential Revision: D9696905

fbshipit-source-id: 2daf24e76c3b3c37aa36cd1540e54876a367faf7

React/Fabric/Mounting/ComponentViews/Text/RCTParagraphComponentView.mm

@@ -84,4 +84,28 @@ using namespace facebook::react;
   return RCTNSStringFromString(_paragraphLocalData->getAttributedString().getString());
 }
 
-@end
+- (SharedTouchEventEmitter)touchEventEmitterAtPoint:(CGPoint)point
+{
+  if (!_paragraphLocalData) {
+    return _eventEmitter;
+  }
+
+  SharedTextLayoutManager textLayoutManager = _paragraphLocalData->getTextLayoutManager();
+  RCTTextLayoutManager *nativeTextLayoutManager = (__bridge RCTTextLayoutManager *)textLayoutManager->getNativeTextLayoutManager();
+  CGRect frame = RCTCGRectFromRect(_layoutMetrics.getContentFrame());
+
+  SharedShadowNode textShadowNode = [nativeTextLayoutManager getParentShadowNodeWithAttributeString:_paragraphLocalData->getAttributedString()
+                                                                                paragraphAttributes:_paragraphAttributes
+                                                                                              frame:frame
+                                                                                            atPoint:point];
+
+  if (!textShadowNode) {
+    return _eventEmitter;
+  }
+
+  SharedEventEmitter eventEmitter = textShadowNode->getEventEmitter();
+  assert(std::dynamic_pointer_cast<const TouchEventEmitter>(eventEmitter));
+  return std::static_pointer_cast<const TouchEventEmitter>(eventEmitter);
+}
+
+ @end

ReactCommon/fabric/textlayoutmanager/platform/ios/RCTTextLayoutManager.h

@@ -27,6 +27,11 @@ NS_ASSUME_NONNULL_BEGIN
          paragraphAttributes:(facebook::react::ParagraphAttributes)paragraphAttributes
                        frame:(CGRect)frame;
 
+- (facebook::react::SharedShadowNode)getParentShadowNodeWithAttributeString:(facebook::react::AttributedString)attributedString
+                                                        paragraphAttributes:(facebook::react::ParagraphAttributes)paragraphAttributes
+                                                                      frame:(CGRect)frame
+                                                                    atPoint:(CGPoint)point;
+
 @end
 
 NS_ASSUME_NONNULL_END

ReactCommon/fabric/textlayoutmanager/platform/ios/RCTTextLayoutManager.mm

@@ -93,4 +93,30 @@ static NSLineBreakMode RCTNSLineBreakModeFromWritingDirection(EllipsizeMode elli
   return textStorage;
 }
 
+- (SharedShadowNode)getParentShadowNodeWithAttributeString:(AttributedString)attributedString
+                                       paragraphAttributes:(ParagraphAttributes)paragraphAttributes
+                                                     frame:(CGRect)frame
+                                                   atPoint:(CGPoint)point {
+  NSTextStorage *textStorage =
+    [self _textStorageAndLayoutManagerWithAttributesString:RCTNSAttributedStringFromAttributedString(attributedString)
+                                     paragraphAttributes:paragraphAttributes
+                                                    size:frame.size];
+  NSLayoutManager *layoutManager = textStorage.layoutManagers.firstObject;
+  NSTextContainer *textContainer = layoutManager.textContainers.firstObject;
+
+  CGFloat fraction;
+  NSUInteger characterIndex = [layoutManager characterIndexForPoint:point
+                                                    inTextContainer:textContainer
+                           fractionOfDistanceBetweenInsertionPoints:&fraction];
+
+  // If the point is not before (fraction == 0.0) the first character and not
+  // after (fraction == 1.0) the last character, then the attribute is valid.
+  if (textStorage.length > 0 && (fraction > 0 || characterIndex > 0) && (fraction < 1 || characterIndex < textStorage.length - 1)) {
+    RCTSharedShadowNodeWrapper *parentShadowNode = (RCTSharedShadowNodeWrapper *)[textStorage attribute:RCTAttributedStringParentShadowNode atIndex:characterIndex effectiveRange:NULL];
+    return parentShadowNode.node;
+  }
+
+  return nil;
+}
+
 @end