floss: avrcp: introduce uinput library for Floss AVRCP

Introduce a custom uinput library to support Floss AVRCP functionality.
The library will help Floss media interface to create and own a uinput
device to propagate received AVRCP commands as uinput events.

Bug: 240780817
Tag: #floss
Test: verified locally that valid fd can be acquired

Change-Id: I704acc53231ccedac43872afd21decc30a66b65c