This format does not support layers: Flatten, Change Format, Cancel?

[MartinNFuller]

Description
When I open a simple image (PNG etc), then add a layer and try to save, Pinta asks me "This format does not support layers. Flatten image?" I want 3 options: Flatten, Change Format, Cancel. "Change Format" should do the same as "Save As" with the file type set to OpenRaster.

Additional context

[cameronwhite]

That seems like a reasonable idea to me 👍

[esthermichelle]

Hi! I’d like to work on this issue. I’ve reviewed the description and I think I can take it on.

Would you be able to assign it to me?