efl_ui_widget: refactor constructor

efl_ui_widget: refactor constructor

Summary:
first of all, in efl-ui we should probebly ensure that a widget is
always created in a window object. Otherwise we are looking for trouble.

Additionally, calling efl_ui_win_shared_data_get on anything else than a
window object will result in a returned NULL value.
If we are not having a widget parent, there is also not much point in
calling a API that is only defined on the widget base class, so we also
move that away

Reviewers: kimcinoo, raster

Reviewed By: kimcinoo

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D9762