Floss: Define on_scan_result_lost API

This defines on_scan_result_lost callback, which is equivalent to
BlueZ's DeviceLost. This callback is triggered when an advertisement is
no longer fulfilling the criteria of MSFT filters.

Bug: 261482382
Tag: #floss
Test: Manual - Build Floss on Linux

Change-Id: Ie3788e938bf96db3f5b68a64cb5206e4abf8ca26