floss: Sync A2DP and HFP connections

Only one device added event should be triggered per device instead of
one for each profile. Using a timeout mechanism to handle cases that
there is only HFP or A2DP supported.

Tag: #floss
Bug: 225032204
Test: Build, flush, connect and see only one
OnBluetoothAudioDeviceAdded event shown on dbus-monitor
`dbus-monitor --system "destination=org.chromium.cras"`
Also test on a2dp only device.

See logs about device added after 5 seconds timeout.
23:33:40.281358Z INFO btadapterd[18870]: [F8:5C:7D:A9:75:45]: a2dp connected.
...
23:33:45.283232Z WARNING btadapterd[18870]: [F8:5C:7D:A9:75:45]: \
    Add a device with only hfp or a2dp capability after timeout.

BYPASS_LONG_LINES_REASON: Bluetooth likes 120 char lines

Change-Id: I4e1e5ce1c6c20673842e5cc0477d7ad5fa993bd2