vg_json: Set multiple mask from json

vg_json: Set multiple mask from json

Summary:
This patch supports multiple masks for multiple attributes on a layer.
Make main_mask_layer and make each mask EFL_CANVAS_VG_CONTAINER_CLASS and connect them.
main_mask_layer is made for masks
The masks are composited into main_mask_layer in order.
main_mask_layer exists for the intersect option in last order
This can be optimized later, and is created and used temporarily in this patch.

Test Plan:
If there are three masks, they can be created as below.
mask_set(clayer, main_mask);
mask_set(main_mask, mask_1);
mask_set(mask_1, mask_2);
mask_set(mask_2, mask_3);

Reviewers: Hermet

Reviewed By: Hermet

Subscribers: cedric, kimcinoo, #reviewers, smohanty, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8507

Change-Id: I5a75640308a69e8e7e50800ff2444d6078c4fe4d