Improve code coverage for broadcast radio

Added missing unit tests for radio manager, AnnouncementAggregator,
and ProgramInfoCache in broadcast radio service. Also fixed the wrong
returned result for isConfigFlagSupported during illegal state for
HAL 2 broadcast radio client, and refactored the broadcast radio
service to improve code coverage.

Bug: 282031772
Test: atest BroadcastRadioTests
Flag: TEST_ONLY
Change-Id: Ibff9586844f5fa2babec4a43e044332a1cb157c9