Add FileInput implement

[giautm]

Fix for #10 (comment)

on React Native, upload file via:

import { FileInput } from 'apollo-upload-client'

// Example usage
graphql(UPDATE__MUTATION, {
  props: ({ mutate }) => ({
    update: (input) => {
      const clientMutationId = Date.now();

      return mutate({
        variables: {
          input: {
            ...input,
            clientMutationId,
            signature: new FileInput({
                "name": "file_0",
                "type": "image/png",
                "uri": "/Users/admin/Library/Developer/CoreSimulator/Devices/C02A708F-7003-4747-BB09-AA35530AFAC8/data/Containers/Data/Application/44243AD1-906B-4C2E-AC28-6D700BA99609/tmp/ReactABI17_0_0Native/CA1AD1AC-2B6D-47EB-9AE3-528A537E8AC7.png"
            }),
            photos: FileInput.fromArray([{
                "name": "file_1",
                "type": "image/png",
                "uri": "/Users/admin/Library/Developer/CoreSimulator/Devices/C02A708F-7003-4747-BB09-AA35530AFAC8/data/Containers/Data/Application/44243AD1-906B-4C2E-AC28-6D700BA99609/tmp/ReactABI17_0_0Native/CA1AD1AC-2B6D-47EB-9AE3-528A537E8AC7.png"
            }, {
                "name": "file_2",
                "type": "image/png",
                "uri": "/Users/admin/Library/Developer/CoreSimulator/Devices/C02A708F-7003-4747-BB09-AA35530AFAC8/data/Containers/Data/Application/44243AD1-906B-4C2E-AC28-6D700BA99609/tmp/ReactABI17_0_0Native/CA1AD1AC-2B6D-47EB-9AE3-528A537E8AC7.png"
            }]),
          },
        },
      });
    },
  }),
}),

[jaydenseric]

I think our current check is a little too strict as I think name and type is optional for RN file objects. This strategy of using a class would definitely solve the risk of false positives and ease the strictness.

It would make working with RN files a little more complicated, and the bundle size of non RN projects will unfairly increase as the new class has to be imported for the file checks in the extractRequestFiles helper.

I'm leaning towards doing it. This PR needs a bit more polish; I'll jump in where I can.

[jaydenseric]

@giautm do you need me to publish a risky beta to test this out?

[jaydenseric]

This is now live in apollo-upload-client@5.0.0-beta.1 – once verified there are no issues with this release we can move out of of beta.

[giautm]

I checked out, it work fine. :)