Fabric: Using small_vector instead of regular vector in some hot code paths

Summary: The hope is that it will remove many unnececery allocations improving overal perfromance.

Reviewed By: mdvacca

Differential Revision: D14249198

fbshipit-source-id: f0442b3919ccead0582a3190dea0e33d517d85f6

ReactCommon/fabric/attributedstring/AttributedString.cpp

@@ -70,7 +70,7 @@ void AttributedString::prependAttributedString(
       attributedString.fragments_.end());
 }
 
-const std::vector<Fragment> &AttributedString::getFragments() const {
+const Fragments &AttributedString::getFragments() const {
   return fragments_;
 }