[relay-compiler] Generated types for fragment on interface type with inline fragments

I have a [reproduction here](https://github.com/NickDubelman/relay-inline-fragment-repro), where I show that you must do something like
```graphql
fragment App2_animal on Animal {
__typename
... on Cat {
id
name
age
lives
}
... on Dog {
id
name
age
breedDescription
}
}
```

instead of
```graphql
fragment App_animal on Animal {
__typename
id
name
age
... on Cat {
lives
}
... on Dog {
breedDescription
}
}
```

I have read as many issues as I could find in this repo and the ts repo and it seems this is intentional? Why is that the case?