Add UMFileSystemInterface dependency to expo-media-library podspec

[Ashoat]

Why

This is necessary to build expo-media-library in a bare config that uses use_frameworks! in its Podfile on iOS. I think expo-media-library was overlooked in #6503. It uses UMFileSystemInterface here.

Test Plan

This is my first PR to Expo, so not entirely sure how to proceed. I made sure pod install worked.

[lukmccall]

LGTM 🎉
However, you need to commit modified pods files. So, please run pod install and commit changes.

[Ashoat]

For some reason, simply following the CONTRIBUTING.md, making this edit, and then running pod install leads to a whole bunch of untracked files in my working copy. It's hard for me to understand which of these files I need to be committing and which I don't.

I've made an educated guess based on #6503, but would appreciate further guidance if there is something I've missed.

There seems to be some issue where XCode/Cocoapods is generating separate [debug|release].xcconfig files, whereas the existing stuff just has a single .xcconfig for both. Here is what I am seeing in my working copy: https://gist.github.com/Ashoat/0f5602bdad7d77234a493ee0193f200e

[lukmccall]

@Ashoat, I've created a new PR from your - #7861, which contains all the needed files. I believe you may use a different version of cocoapods (we're using 1.8.4).

Thanks for contributing 🎉🥇

Also, I'm closing this PR in favor of the new one.

[Ashoat]

Perfect, thank you @lukmccall. You’re right - I’m on 1.9.1.