[M120 Migration][VD] Support EWK Scroll API for TV WebBrowser

[M120 Migration][VD] Support EWK Scroll API for TV WebBrowser

TV browser team requires below EWK API:

ewk_settings_uses_scrollbar_thumb_focus_notifications_set()
"scrollbar,thumb,focus,changed"

This api is for enhancement of scroll usability from 16' browser:
focus to scrollbar's thumb area -> browser get callback
-> browser set scroll mode (after callback, when get 4way key
input scroll function will do)

Reference:
https://review.tizen.org/gerrit/#/c/291432/

Change-Id: I954b179ad36107118c131ff1a6a850d84ec09343
Signed-off-by: wangjing <jing124.wang@samsung.com>