Case sensitive enum values

When an XSD file as the following value
```xml
<xs:enumeration value="TODO" />
<xs:enumeration value="todo" />
```

The code generated becomes

```proto
enum ModelType {
  // Default
  MODEL_TYPE_UNSPECIFIED = 0;
  MODEL_TYPE_TODO = 1;
  MODEL_TYPE_TODO = 1;
}
```

How could this be mitigated?