Floss: Implement StartScan and StopScan with filter

* Wire Floss daemon to use btif's MSFT API
* Create AsyncHelper to provide abstraction for async call to btif.
* Tweak the BTIF MSFT API to accept call_id in every call so that Floss
  daemon can track which callback is for which caller.
* BTIF implementations are still placeholders. Next follow up will
  implement the real ones after the low layer support is checked in.

Bug: 217274432
Tag: #floss
Test: Manual - Test LE Scan with btclient
BYPASS_LONG_LINES_REASON: Bluetooth likes 120 lines

Change-Id: Ie9813aa5f9a88735227450207f69f7487a6086ab