file-info: Add a set of attributes for large thumbnails

Some applications (eg., gnome-photos) really want a large thumbnail, if one can be created. Simply falling back to a smaller one (probably created by an old nautilus), without giving the application a chance to create a bigger thumbnail, is undesirable because they will appear fuzzy.

Therefore, at separate attribute sets for all the thumbnail sizes that are supported in the spec: normal/large/xlarge/xxlarge.

This picks up 7 year old patches by Debarshi from #621 (closed) in an attempt to address the immediate needs in #2767 (closed).