Fix gc of async destructuring assignments of strings (#5126)

This fixes #5089

When garbage collection is running on a paused async function that
includes destructuring assignments of strings, the string can be a
direct string, and not an object, which cannot be marked as visited, as
it does not have a visited flag.

JerryScript-DCO-1.0-Signed-off-by: Máté Tokodi mate.tokodi@szteszoftver.hu

tests/jerry/regression-test-issue-5089.js

@@ -0,0 +1,27 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+async function test1() {
+    var a;
+    ({k: a = await 1} = "XY");
+}
+test1();
+gc();
+
+async function test2() {
+    var a;
+    [a = await 1] = "";
+}
+test2();
+gc();