ui.box_flow: refactor layout_update
Summary:
This patch remove evas_box function from Efl.Ui.Box_Flow and add unit test.
Depends on D8214
Test Plan:
- make check
- elementary_test -to 'efl.ui.box' with 'flow' checkbox.
Reviewers: zmike, Jaehyun_Cho
Reviewed By: zmike
Subscribers: cedric, reviewers, committers
Tags: efl
Differential Revision: https://phab.enlightenment.org/D8219