`relay-compiler` generates invalid Typescript for `@raw_response_type` + combination of conditional and non-conditional fragments

Given the code below:

```ts
export const query = graphql`
query AppQuery($showEmail: Boolean!) @raw_response_type {
...AppFragment
...AppConditionalFragment
}
`;

export const fragment = graphql`
fragment AppFragment on Query {
account {
name
}
}
`;

export const conditionalFragment = graphql`
fragment AppConditionalFragment on Query {
account @include(if: $showEmail) {
email
}
}
`;
```

Relay compiler generates the following types (notice the `account` field is listed twice):
```ts
export type AppQuery$rawResponse = {
readonly account: {
readonly id: string;
readonly name: string;
} | null | undefined;
readonly account: {
readonly email: string;
} | null | undefined;
};
```

Which typescript interprets by using the first declaration of a given field and ignoring all others, leading to errors like:

This very reproduction can be found at https://github.com/vhfmag/relay-ts-typegen-issue-repro

Instead, relay compiler should generate something like:
```ts
export type AppQuery$rawResponse = {
readonly account: {
readonly id: string;
readonly name: string;
readonly email?: string | null | undefined;
} | null | undefined;
};
```

Start with the linked relay-ts-typegen-issue-repro and inspect the generated AppQuery$rawResponse type for the duplicate account fields. Trace the relay-compiler path that combines conditional and non-conditional fragment selections under @raw_response_type, then add a regression test showing one merged account field with email optional and verify the generated TypeScript.

Written by the indexing model from the issue text.