fix: TS make DocumentPickerResponse a single response

[GertjanReynaert]

Summary

When using pickSingle TS incorrectly expects us to array destructure the response, which shouldn't be the case for a single response.

Since everywhere in the codebase DocumentPickerResponse[] is used where it is expected to be an array, the current Array<{...}> notation causes TS to mark this as a nested array, instead of just an array.

In this PR I've removed the Array<> notation, making the pickSingle having a single response, and the pickMultiple still having it's array response.

Test Plan

yarn typescript

What's required for testing (prerequisites)?

What are the steps to reproduce (after prerequisites)?

Compatibility

OS	Implemented
iOS	✅
Android	✅

Checklist

• I have tested this on a device and a simulator
• I added the documentation in README.md
• I updated the typed files (TS and Flow)

[vonovak]

ah, sorry about this; thanks for the PR!