[native] hide native-specific code
Summary:
Hiding code that will require adding to web dependencies like olm.h or SecureStore implementation.
NOTE: Using #ifdef is not the cleanest and this will be refactored, native-only code will be extracted, but this requires breaking changes and will take some review cycles, that being said I want to port this on web and make it workable (this is the goal) and right after I will put up diffs with refactor.
Depends on D8549
Test Plan: yarn build-db-wasm
Reviewers: michal, tomek, jon
Reviewed By: michal
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D8550