Fix the value of the caller property of function instances (#4258)

We do not support the caller information for functions, and since a
'null' value represents that there has been no caller, the default value
should be changed to 'undefined' to signal that the information is not
available.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai daniel.batyai@h-lab.eu

tests/jerry/es.next/function-arguments-caller.js

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-var props = ['arguments', 'caller'];
-
 function f_simple () {
 }
 
@@ -21,27 +19,48 @@ function f_strict () {
   "use strict";
 }
 
-for (let prop of props) {
-  try {
-    Function.prototype[prop];
-    assert(false);
-  } catch (e) {
-    assert(e instanceof TypeError);
-  }
-
-  assert(f_simple[prop] === null);
-
-  try {
-    f_strict[prop];
-    assert(false);
-  } catch (e) {
-    assert(e instanceof TypeError);
-  }
-
-  let desc = Object.getOwnPropertyDescriptor(f_simple, prop);
-  assert(desc.value === null);
-  assert(desc.writable === false);
-  assert(desc.enumerable === false);
-  assert(desc.configurable === false);
-  assert(Object.getOwnPropertyDescriptor(f_strict, prop) === undefined);
+try {
+  Function.prototype["arguments"];
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
 }
+
+assert(f_simple["arguments"] === null);
+
+try {
+  f_strict["arguments"];
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+let desc = Object.getOwnPropertyDescriptor(f_simple, "arguments");
+assert(desc.value === null);
+assert(desc.writable === false);
+assert(desc.enumerable === false);
+assert(desc.configurable === false);
+assert(Object.getOwnPropertyDescriptor(f_strict, "arguments") === undefined);
+
+try {
+  Function.prototype["caller"];
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+assert(f_simple["caller"] === undefined);
+
+try {
+  f_strict["caller"];
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+desc = Object.getOwnPropertyDescriptor(f_simple, "caller");
+assert(desc.value === undefined);
+assert(desc.writable === false);
+assert(desc.enumerable === false);
+assert(desc.configurable === false);
+assert(Object.getOwnPropertyDescriptor(f_strict, "arguments") === undefined);