[CommCoreModule] Introduce SocketStatus enum

Summary:

1. Introduce SocketStatus type (defaulted to the same four states as readyState for now.. can always reassess later if we need to represent some other state)
2. Add SocketStatus socketStatus to NetworkModule as a public member
3. Add GlobalNetworkSingleton::getSocketStatus() getter to retrieve the networkModule socket status

Test Plan: Was able to call comm::GlobalNetworkSingleton::instance.getSocketStatus(); outside of a scheduleOrRun and got back expected response.

Reviewers: ashoat, def-au1t, palys-swm, karol-bisztyga

Reviewed By: ashoat, karol-bisztyga

Subscribers: Adrian, benschac

Differential Revision: https://phabricator.ashoat.com/D3066