add GS_GUI_OPT_BRINGTOFRONT

[Samdal]

Instead of needing to manually set the container — if you want a pop-up for example, you could set an opt instead.

This would in part do the same as
GS_API_DECL void gs_gui_bring_to_front(gs_gui_context_t *ctx, gs_gui_container_t *cnt);