HearingAidService: Fix first connection to a device

* Always connect to the target device itself, even if no HiSyncId
* Don't disconnect before connect if no HiSyncId info
* Clear HiSyncId and capabilities map during service start and stop
* Add debug log message for OnDeviceAvailable stack event

Test: instrumentation test
Bug: 69623109
Change-Id: Idbf43561331cfbf9c512f4b37b1a83ad118c2f4f