The new GPU_SHADER_2D_WIDGET_BASE shader allows us to draw many complex shapes with anti-aliasing. One thing it can do is draw an opaque rounded rectangle with colors that differ between its interior and outline. In order to do the above in a single pass I recently added an "_ex" version of UI_draw_roundbox that exposes most of that shaders features. This simplifies interface_draw.c by removing redundancy in the calling of this shader by using this new uber "_ex" version. Ref D10189