PLAT-14806: Add accessibilityValueText for reading custom string
PLAT-14806: Add accessibilityValueText for reading custom string

TV can read only simpleIntegerPicker's value and unit whenever
value or unit is changed, so accessibilityValueText is necessary for
reading other custom string.

https://jira2.lgsvl.com/browse/PLAT-14806
Enyo-DCO-1.1-Signed-off-by: Bongsub Kim <bongsub.kim@lgepartner.com>

Change-Id: I0373ada96ecc5282b69ba6d46602b7338b6adeb8

enyojs/moonstone