Only create NSAttributedString if NSTextStorage is nil (facebook#36773)

Summary:
Pull Request resolved: facebook#36773

Changelog: [internal]

Do not construct `NSAttributedString` if `NSTextStorage` exists. Creating `NSAttributedString` is expensive and it isn't needed to measure text if `NSTextStorage` `exists`

Reviewed By: cipolleschi

Differential Revision: D44620292

fbshipit-source-id: 0827c514e40fcbd9626d2b7d7b6d28a3332d9aa1

Author: sammy-SC

packages/react-native/ReactCommon/react/renderer/textlayoutmanager/platform/ios/react/renderer/textlayoutmanager/RCTTextLayoutManager.mm

@@ -64,10 +64,14 @@ - (TextMeasurement)measureAttributedString:(AttributedString)attributedString
                          layoutConstraints:(LayoutConstraints)layoutConstraints
                                textStorage:(NSTextStorage *_Nullable)textStorage
 {
-  return [self measureNSAttributedString:[self _nsAttributedStringFromAttributedString:attributedString]
-                     paragraphAttributes:paragraphAttributes
-                       layoutConstraints:layoutConstraints
-                             textStorage:textStorage];
+  if (textStorage) {
+    return [self _measureTextStorage:textStorage];
+  } else {
+    return [self measureNSAttributedString:[self _nsAttributedStringFromAttributedString:attributedString]
+                       paragraphAttributes:paragraphAttributes
+                         layoutConstraints:layoutConstraints
+                               textStorage:nil];
+  }
 }
 
 - (void)drawAttributedString:(AttributedString)attributedString