Added SystemApi annotation to REASON_BLUETOOTH_BROADCAST

As Android Bluetooth becomes a mainline module, we need to
remove all hidden API usages. BluetoothManagerService is
using REASON_BLUETOOTH_BROADCAST so we have to make it
accessible to the Bluetooth module.

Tag: #feature
Bug: 211851706
Test: make
Change-Id: I99ade4673836c068b2e643ce5e56d9ad0454233f