EditorExportPlatformAndroid object doesn't contain expected properties at export time

### Tested versions

- Reproducible in Godot 4.2.1.stable

### System information

Windows 11 - Android 13 export

### Issue description

I have an Android export plugin where I am overriding `_get_android_manifest_application_element_contents()` and trying to get the `package/unique_name` property from the `EditorExportPlatformAndroid` object as follows:

```
class AndroidExportPlugin extends EditorExportPlugin:
...
func _get_android_manifest_application_element_contents(platform: EditorExportPlatform, debug: bool) -> String:
...
if platform is EditorExportPlatformAndroid:
var __unique_name = platform.get("package/unique_name")
```

However, the `package/unique_name` property is not set in the `platform` argument object.

`platform.get("package/unique_name")` returns `null`.

### Steps to reproduce

- Open MRP in Godot Editor
- Install Android build template
- Debug MRP on an Android device
- Check console output

### Minimal reproduction project (MRP)

[editor-export-platform.zip](https://github.com/godotengine/godot/files/14157093/editor-export-platform.zip)

Start by running the attached editor-export-platform.zip reproduction with the stated Godot 4.2.1 setup, then trace the _get_android_manifest_application_element_contents() callback and inspect the EditorExportPlatformAndroid argument. Done means establishing and correcting the availability of package/unique_name at export time, with the reproduction no longer reporting null.

Written by the indexing model from the issue text.