Support "req.formData()"

Prerequisites

• I confirm my issue is not in the opened issues
• I confirm the Frequently Asked Questions didn’t contain the answer to my issue

Environment check

• I’m using the latest msw version
• I’m using Node.js version 14 or higher

Node.js version

16.13.0

Reproduction repository

https://github.com/ddolcimascolo/msw-issue-1327

Reproduction steps

Axios to send a POST request with a FormData body. Try to use req.body in the handler

Current behavior

TypeError: The "input" argument must be an instance of ArrayBuffer or ArrayBufferView. Received an instance of FormData
        at new NodeError (node:internal/errors:371:5)
        at TextDecoder.decode (node:internal/encoding:413:15)
        at decodeBuffer (/data/dev/msw-issue-formdata/node_modules/@mswjs/interceptors/src/utils/bufferUtils.ts:11:18)
        at RestRequest.get body [as body] (/data/dev/msw-issue-formdata/node_modules/msw/src/utils/request/MockedRequest.ts:117:18)

Expected behavior

Maybe req.formData() as per https://developer.mozilla.org/en-US/docs/Web/API/Request/formData would be the way to go?

[nathanhannig]

I have been stuck at 0.43.1 because of this isse

req.body was broken after that version (even though it incorrectly says it was depreciated)

[kettanaito]

@ddolcimascolo, no news so far. Anybody is welcome to take the reproduction repo above and step through this body function to find out what happens now with FormData bodies. Debugging this is about 80% of solving it.