NONE: fix processing large file jsons from get file

[Roystbeef]

We were running into Cannot create a string longer than 0x1fffffe8 characters errors that we were able to pinpoint to the response.data call when calling get file.

This is because the JSON string that gets returned from Figma can be over 512 MB in length. So instead of treating it as a single string, this PR updates that logic so we stream in and build up the JSON object for the file.

Test Plan

• Create a very large file in Figma
• Try to attach the file to an issue
• Previously see that that it throws the error above
• With the changes, see that it's able to successfully parse the file json
• Assert that existing tests pass