Add new callback to inform blocking of network on specific uid.

Currently, apps rely on querying NetworkInfo object to know
whether their network is blocked or not. There is no proactive
way to tell app when it is being blocked/unblocked. The only
event that app would receive is SocketException with
ECONNABORTED when their ongoing socket connection has been
blocked, which is not an elegant way to notify app.

Thus, this commit is trying to address this problem. Therefore,
with the uses of other callbacks, the need of
getState/getDetailedState in NetworkInfo could be completely
eliminated.

Test: runtest frameworks-net
      runtest -x NetworkPolicyManagerServiceTest.java
      cts-tradefed run cts -m CtsHostsideNetworkTests
      cts-tradefed run cts -m CtsNetTestCases -t \
              android.net.cts.ConnectivityManagerTest
Bug: 74575553

Change-Id: Iec96a3103d0aa9a505020eb89d69b89c0b694486