Comment 6 for bug 2001708

After doing some searching around, the flatpak for evince previously did this by overwriting the default loaders.cache from gdk-pixbuf (not sure if snap allows this). The new approach seems to be calling gdk_pixbuf_init_modules() from the application to load some additional pixbuf plugins from a specific directory. The latter seems like a cleaner solution, although I think that requires manually building webp-pixbuf-loader as well when building the snap