Create SystemApi for statsd ready broadcast

The statsd ready broadcast needs to be sent from statsd apex with
Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND flag that is @hide and cannot be
promoted to @SystemApi.
In R, this was worked around by getting the list of registered broadcast
receivers and sending them directed broadcasts to wake them up in
ag/10404099.
However, this is inefficient if there are multiple receivers so this
change creates a SystemApi for sending the actual broadcast with the
flag as recommended in ag/10404099 after it was submitted.

Bug: 150746848
Test: m
Test: flash
Test: ensure broadcast is received via logcat
CTS-Coverage-Bug: 184014462

Change-Id: I5103d8c6e87bdb47930cb7457731050da3d8e566