[M120 Migration][VD] Support ewk apis of key event

[M120 Migration][VD] Support ewk apis of key event

1.Support ewk apis of key event in case some other application will use
it.
Support ewk_view_send_key_event & ewk_view_key_events_enabled_set.
ewk_view_key_events_enabled_set:
EINA_FALSE---delete keydown and keyup callback in chromium
EINA_TRUE----add keydown and keyup callback in chromium
If callback is delete, WRT use ewk_view_send_key_event to send
keydown and keyup event to chromium.
Currently WRT dose not use ewk interface, but we keep this API in case
some other application will use it.

2.Add ewk_view_send_key_event to internal API header

refer:
https://review.tizen.org/gerrit/#/c/291454

Change-Id: I257fa7491efacb20b192fccfec1378d4630862cf
Signed-off-by: fang fengrong <fr.fang@samsung.com>