Relay Resolvers named imports consistency

Love the progress on resolvers - looks like they'll open up a lot of options for us.

With `use_named_imports_for_relay_resolvers` enabled....

1. There's nothing checking that the field name you use matches the exported function name, which leads to importing names that don't exist
```ts
/**
* @RelayResolver Query.example: String
*/
export function other(){}
```
```js
import { example as ... } from ...
// should instead be
import { other as ... } from ...
```
But this should probably be a validation error.

2. There's potential accidentally use a `default export`, even though `use_named_imports_for_relay_resolvers` switched the behaviour
```
/**
* @RelayResolver Query.example: String
*/
export default function example(){}
```
```
import { example as ... } from ...
```
But `example` wasn't exported. This should also be a validation error.

Start by locating the implementation of use_named_imports_for_relay_resolvers and the resolver validation or import-generation tests. Trace how the RelayResolver field name maps to an exported function, including default exports. Done means mismatched names and default exports produce validation errors instead of invalid named imports.

Written by the indexing model from the issue text.