[native] Export neynarKey so it's accessible from native

Summary: Making neynarKey in native/facts available throughout native app.

Test Plan:

1. Imported neynarKey in PrivacyPreferences
2. Displayed neynarKey in Text component and ensured it was as expected

Reviewers: ashoat, ginsu, tomek, will, varun

Reviewed By: ginsu

Differential Revision: https://phab.comm.dev/D11380