Taxonomy Alias field is ignored when generating annotation output data

# Describe the bug
With the control tag ``, when Label Studio generates the annotation output data, the `value` field of `` is used instead of the `alias` field.

This problem doesn't exist with the control tag ``.

# To Reproduce
[In the Label Studio playground](https://labelstud.io/playground/), run those two test cases:
## 1. Choices = OK
```xml

```

## 2. Taxonomy = NOT OK
```xml

```

# Expected behavior
The annotation output data should use the `alias` field instead of the `value` field. In test case 2 above, the annotation output should be:
```json
[
{
"value": {
"taxonomy": [
[
"001"
]
]
},
"id": "OXNSOGlB5U",
"from_name": "MyControlTag",
"to_name": "MyObjectTag",
"type": "taxonomy"
}
]
```