evas proxy: make it work for load_region

evas proxy: make it work for load_region

Summary:
This makes a proxy object use a selective region of a source object.
So far a proxy has not worked for load_region at all.
This should be better solution than https://phab.enlightenment.org/D10604
introducing new interface.

This is useful when the source is too big to allocate a proxy surface.
This will be used by elm_scroller to solve following issue.

[Issue]
If size of elm_sclloer content is too big, then the proxy of
elm_scroller to show loop effect does not work. Because
evas_gl_common_image_surface_new does not allow
bigger size surface than max_texture_size

Reviewers: Hermet, jsuya

Reviewed By: Hermet

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D10626

Change-Id: I9a8d80eca88a5f2d1d1c1b5425294bcd4017bfa9