DO NOT MERGE: Add unit tests to ensure VPN meteredness

These new tests ensure that VPNs report the meteredness of their
underlying networks correctly. The added test verifies VPN meteredness
for cases of metered and unmetered WiFi and Cell

Bug: 78644887
Test: This; ran on walleye-eng
Change-Id: I28bdc71a336bfd97f7908455d4781d774df44b87