Allow unprivileged NetworkCallbacks to see other UIDs' networks.

Currently, unprivileged apps can call getAllNetworks() to see
all networks on the system, even networks that do not apply to
them. Allow them to do this via NetworkCallbacks as well.

This is the last piece of information that was only available
through getAllNetworks, so this CL deprecates that API.

Bug: 187921303
Test: new unit tests
Test: CTS test in other CL in topic
Change-Id: I30f1021927d3c8eae6525116c61ff4a4acecff6d