Merge pull request #3425 from tanadeau/sr-1952-add-escaping-parsing

[WIP][Parser][SR-1952] Added @escaping attribute parsing

lib/Serialization/Serialization.cpp

@@ -2951,6 +2951,7 @@ void Serializer::writeType(Type ty) {
            fnTy->isAutoClosure(),
            fnTy->isNoReturn(),
            fnTy->isNoEscape(),
+           fnTy->isExplicitlyEscaping(),
            fnTy->throws());
     break;
   }