Volume slider content description

Volume, ring and acessibility sliders now report their names
when talk back is on.

Examples:
26% acessibility seek control, use volume keys to adjust.
0% ring seek control, disabled.

Change-Id: I0a775a9b90254c9f338b9f4f38efbff10f626853
Fixes: 62354047
Test: Turn talk back on, tap on volume sliders