[native] more blocking functions

Summary:
Included all of these functions in a single diff because they all do the same thing - block the tokio runtime on the completion of their equivalent async fns

Depends on D4936

Test Plan: tested in the following diff where we expose these blocking functions in the ffi module

Reviewers: tomek, karol, atul

Reviewed By: tomek

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D4937