Limit visibility of libfmq_rust while under development

Preventing uses of the library ensure we can still easily make changes
to the APIs. The visibility restrictions will be removed once the
library is finished.

Test: m
Test: add libfmq_rust to android.hardware.lights-service.example
Test: make sure build fails due to visibility
Bug: 294698705
Change-Id: Ia9dabed3eb6be4cb15767829edd04e77ec9d9274
1 file changed