Fabric: Propper support for `accessibilityLabel` in RCTParagraphComponentView

Summary:
@public
This approach is basically copying exising implementation that we have in RCTTextView (D5806097).
Changes in `AttributedString` is quite trivial.

Reviewed By: mdvacca

Differential Revision: D8740000

fbshipit-source-id: 276afdf93d777f7ccb99ca8ee5a18a880de2acbf

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

@@ -68,4 +68,20 @@ using namespace facebook::react;
                                           frame:frame];
 }
 
+#pragma mark - Accessibility
+
+- (NSString *)accessibilityLabel
+{
+  NSString *superAccessibilityLabel = [super accessibilityLabel];
+  if (superAccessibilityLabel) {
+    return superAccessibilityLabel;
+  }
+
+  if (!_paragraphLocalData) {
+    return nil;
+  }
+
+  return RCTNSStringFromString(_paragraphLocalData->getAttributedString().getString());
+}
+
 @end

ReactCommon/fabric/attributedstring/AttributedString.cpp

@@ -39,6 +39,14 @@ const std::vector<Fragment> &AttributedString::getFragments() const {
   return fragments_;
 }
 
+std::string AttributedString::getString() const {
+  std::string string;
+  for (const auto &fragment : fragments_) {
+    string += fragment.string;
+  }
+  return string;
+}
+
 #pragma mark - DebugStringConvertible
 
 SharedDebugStringConvertibleList AttributedString::getDebugChildren() const {

ReactCommon/fabric/attributedstring/AttributedString.h

@@ -61,6 +61,11 @@ public:
    */
   const Fragments &getFragments() const;
 
+  /*
+   * Returns a string constructed from all strings in all fragments.
+   */
+  std::string getString() const;
+
 #pragma mark - DebugStringConvertible
 
   SharedDebugStringConvertibleList getDebugChildren() const override;