Add AudioSystem.listDeclaredDevicePorts method

This is useful for tests that exercise external device
connection/disconnection scenarios. 'listAudioPorts'
returns ports for currently connected devices only.

Bug: 273252382
Test: atest audiopolicymanager_tests
Change-Id: I7d235d993235e21696002448ebf09b27ad6955a6
Merged-In: I7d235d993235e21696002448ebf09b27ad6955a6