battery: Implement Battery Provider API

battery: Implement Battery Provider API

This patch implements the BatteryProvider1 and BatteryProviderManager1
API. This is a means for external clients to feed battery information to
BlueZ if they handle some profile and can decode battery reporting.

The battery information is then exposed externally via the existing
Battery1 interface. UI components can consume this API to display
Bluetooth peripherals' battery via a unified BlueZ API.

Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>