Enum types are not being generated by the Typescript Generator

**API Platform version(s) affected**: 3.0

**Description**
I'm using the Typescript Generator to generate some interfaces and I have some enum types in the Entity, for example:
```php

The generator should generate the corresponding enum and implement it in the interface:

```ts
export interface Person {
...
gender?: gender;
...
}

export enum gender {
FEMALE = 'female',
MALE = 'male',
}
```

**Additional Context**