DO NOT MERGE: Fix ConnectivityController meteredness checks

This patch corrects ConnectivityController's meteredness checks to
perform correct meteredness checks while VPNs are running. This fixes a
bug in O-MR1 where any apps using the DownloadProvider with unmetered
network constraints fail to start while the VPN is enabled.

This change adds a bespoke method for ConnectivityController, allowing
it to correctly identify the meteredness without affecting public API
surfaces.

Bug: 78644887
Test: Built, flashed on Walleye, and tested.
Test: Additional test coverage in subsequent patch(es).
Change-Id: Ie1d11d93d51d936ce81cd5984af61bde30325983