[native] [38/40] RN 0.70: Update to react-native-fs@2.20.0

Summary:
npx @rnx-kit/dep-check --write recommended upgrading this package (albeit to a lower version).

Depends on D5938

Test Plan:

1. I reviewed the Release Notes and found no breaking changes
2. I tested a bunch of react-native-fs stuff relating to media on both iOS and Android
3. Tested along with whole stack: test plan (includes saving media)

Reviewers: tomek, bartek

Subscribers: atul

Differential Revision: https://phab.comm.dev/D5939