When source is not added by the current phone (for example during...

When source is not added by the current phone (for example during multi-point), we won't be able to sync and desync, so we don't show play pause button.

Flag: com.android.settingslib.flags.audio_stream_play_pause_by_modify_source
Test: atest
Bug: 384976631
Change-Id: I9119db063cfe3ed980f89b0799e0e1c7a1d6a3e1