e_client: move e_focus_event_mouse_down() at e_client_mouse_down

e_client: move e_focus_event_mouse_down() at e_client_mouse_down

It shows the before and after call flow for e_focus_event_mouse_down.
BEFOER : _e_comp_wl_evas_cb_mouse_down() -> e_focus_event_mouse_down()
AFTER  : _e_comp_object_cb_mouse_down() -> e_client_mouse_down() -> e_focus_event_mouse_down()

Other e_focus_mouse apis(e_focus_mouse_up/move) is called through
e_client_mouse apis(e_client_mosue_up/move), so e_focus_event_mouse_down()
is also changed to be called through e_client_mouse_down().

Change-Id: I189967b67d0a3dd373418990476daac97ec4a803