efl: Introduce Eina.Rect and switch EO APIs to it

efl: Introduce Eina.Rect and switch EO APIs to it

It's a complex struct but defined in EO as a simple struct. ABI-wise
it's equivalent to Eina_Rectangle. Some macros that use Eina_Rectangle
also work on Eina_Rect out of the box, most of the code dealing with
x,y,w,h will require no modifications either.

But Eina_Rect provides direct access to a size or position 2d component,
as well as the usual x,y,w,h. The field "rect" is provided as a
convenience for code dealing with both Eina_Rectangle and Eina_Rect. We
may or may not require it.

Note: Size2D could use unsigned values but I have spotted a few places
in the code that actually use -1 to indicate invalid size (as opposed to
0x0).

@feature