LibJS: Make Object.getOwnPropertyDescriptor() work with string indexed property

E.g. for "0" we have to contruct a PropertyName with Type::Number so it
looks in the indexed properties as expected.

Userland/Libraries/LibJS/Runtime/Object.cpp

@@ -388,6 +388,11 @@ Optional<PropertyDescriptor> Object::get_own_property_descriptor(const PropertyN
         value = existing_value.value().value;
         attributes = existing_value.value().attributes;
     } else {
+        if (property_name.is_string()) {
+            i32 property_index = property_name.as_string().to_int().value_or(-1);
+            if (property_index >= 0)
+                return get_own_property_descriptor(property_index);
+        }
         auto metadata = shape().lookup(property_name.to_string_or_symbol());
         if (!metadata.has_value())
             return {};

Userland/Libraries/LibJS/Tests/builtins/Object/Object.getOwnPropertyDescriptor.js

@@ -43,6 +43,24 @@ test("setter property", () => {
     expect(o).toHaveSetterProperty("foo");
 });
 
+test("indexed property", () => {
+    let o = { 0: "foo" };
+
+    expect(o).toHaveConfigurableProperty(0);
+    expect(o).toHaveEnumerableProperty(0);
+    expect(o).toHaveWritableProperty(0);
+    expect(o).toHaveValueProperty(0, "foo");
+    expect(o).not.toHaveGetterProperty(0);
+    expect(o).not.toHaveSetterProperty(0);
+
+    expect(o).toHaveConfigurableProperty("0");
+    expect(o).toHaveEnumerableProperty("0");
+    expect(o).toHaveWritableProperty("0");
+    expect(o).toHaveValueProperty("0", "foo");
+    expect(o).not.toHaveGetterProperty("0");
+    expect(o).not.toHaveSetterProperty("0");
+});
+
 test("defined property", () => {
     let o = {};