Fire ConnectivityDiagnostics callbacks on Connectivity reported.

When ConnectivityService#reportNetworkTested is called, the platform
needs to fire ConnectivityDiagnostics callbacks for registered callbacks
that are permissioned for the network being reported on. This adds a new
event to ConnectivityDiagnosticsHandler for invoking these callbacks.

Bug: 143187964
Test: compiles
Test: atest CtsNetTestCases ConnectivityServiceTest
Change-Id: Icc6bcf7a2411133d8ecd7477bc351dad9333f24f
(cherry picked from commit 3d57b0f4ff5b56780c79df6062dfaf2b9fa5ae3c)