floss: Implement BLE advertising methods and callbacks

This patch wires IBluetoothGatt/IAdvertisingSetCallback to topshim and
use GattStatus for status used in advertising set callbacks.

It also introduces new btclient command "advertise [on|off]" to verify
the D-Bus methods StartAdvertisingSet and StopAdvertisingSet and their
callbacks.

Bug: 233128394
Tag: #floss
Test: build.py --target test
Test: bclient advertise [on|off]

Change-Id: I28f7b9af5a599b6a48af80f5f10c514a2bdae0e0