[native] Move CommSecureStore::get to main thread to avoid JNI crash

Summary:
This is option 2 from this Linear comment.

Depends on D6957

Test Plan:
Test that the error goes away in favor of another see (see Linear)

Also need to test this on iOS before landing to make sure it doesn't break that, but should be okay

Reviewers: atul, marcin

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D6958