Objects in List Properties are Incorrectly Exported As Integers to Lua

### Describe the bug

When adding an "object" inside a "list" property, the object with id `n` is incorrectly exported as `n`, instead of `{ id = n }`.

### Steps to reproduce

create a new map and object layer
create two objects, which get the ids `1` and `2`
add the following properties to `object 1`:
`object.obj`: an "object" property, pointing to `object 2`
`object.int`: an "int" property, set to `2`
`object.list`: a "list" property
`object.list[0]`: an "object" property, pointing to `object 2`
`object.list[1]`: an `int` property, set to `2`

This map exports with the following object layer to lua:

```lua
objects = {
{
id = 1,
name = "",
type = "",
shape = "rectangle",
x = 1.11836,
y = 2.33686,
width = 5.39148,
height = 3.22153,
rotation = 0,
opacity = 1,
visible = true,
properties = {
["list"] = {
2,
2
},
["obj"] = { id = 2 },
["int"] = 2
}
},
```

`object.obj` is exported as `{ id = 2 }`, but `object.list[0]`, which is an "object" property pointing to the same object, is exported as `2`, not `{ id = 2 }`. Because the object inside the list is exported as an integer, there is no way to distinguish an object with id `n` inside a list and the integer `n` inside a list.

### Expected Behavior

The map should export as:

```lua
objects = {
{
id = 1,
...
properties = {
["list"] = {
{ id = 2 },
2
},
["obj"] = { id = 2 },
["int"] = 2
}
},
...
```

### OS version

Windows 11

### Tiled version

1.12.2

No source file or test is named. Reproduce the issue with the described map and trace the Lua export path for object and list properties; done means object references inside lists export as `{ id = n }` while integer entries remain integers.

Written by the indexing model from the issue text.