ecore_evas: add API for finding out if event is used

ecore_evas: add API for finding out if event is used

Summary:
ecore_x_dnd_send_status can be used to indicate if a item can be dropped
on a client or not. However, we should only indicate that this can be
dropped, if there is a object we signaled that a drop is in.

Long story short: there is no assertion that after indicating that
things can be dropped, that a notify for the data is sent. A drag
implementation should always listen to a mouse up event, and abort the
drag if no further operations are sent.
Depends on D11698

Reviewers: zmike, stefan_schmidt, raster

Reviewed By: zmike

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D11699