[lib] Add getAvatarURIForAddress to ENSCache
Summary:
This method will allow us to query the cache for ENS avatars.
Depends on D7040
Test Plan:
- Test plan described here, implemented via unit tests in following diffs
- Tested SVGs in React Native as noted here
Reviewers: atul
Reviewed By: atul
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D7041