Add support for esmodules for provided variables

[bigfootjon]

Fixes: #3966

I based my implementation on 0c4108d and efd9d86

Not great that we're duplicating the code for this around the codebase, happy to clean things up if anyone has any ideas.

Test plan:

??? I'm not really sure how to use this for my personal project locally and the test suite doesn't have any existing tests and my knowledge of Jest is... lacking.

[captbaritone]

Thanks!

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[mofeiZ]

Thanks for trying out provided variables + helping us making this more usable for open source!

I think we'll also need to add type generation changes in the relay-typegen crate. Relay generate types for every provided variable used by a query to ensure that the provider module (1) exists and (2) exports a function of the correct type.

• The code lives insrc/write.rs ->generate_provided_variables_type

The current TypeScript (+ flow) type-generation would produce types that look like this:

// graphql`
//  fragment Foo @argumentDefinitions(x : {type: "Float", provider: "getValue"}) {
//    my_field(arg: $x)
//  }
type ProvidedVariablesType = {
  readonly __relay_internal__pv__getValue: {
    readonly get: () => number | null;
  };
};

const providedVariablesDefinition: ProvidedVariablesType = {
  "__relay_internal__pv__getValue": require('./getValue')
};

[captbaritone]

@bigfootjon are you still interested in working on this? If not we can close it.

[bigfootjon]

Yeah sorry I don’t have the bandwidth to finish this :(