Add unit test for IRadioService implementation

Unit tests are added to test BrodacastRadioService implementation.
Mockito library and debuggable setting in manifest file are
modified to supoort mocking final classes and non-public methods.

Bug: 241118988
Test: atest com.android.server.broadcastradio
Change-Id: I2f664ded7ccbcb17e1de6363db6833ea7b3e7a53