Show audio sharing button and qs dialog improvement when preview enabled

Also listen to `onBroadcastMetadataChanged` instead of `onPlaybackStarted` for hysteresis mode

Test: atest
Bug: 368401233
Flag: com.android.settingslib.flags.audio_sharing_developer_option
Change-Id: I9b99a5a5f3c00cf72e2204d6d3398bfe82019015