Gtk.Picture should allow configuration of resize interpolation method

Gtk.Picture can resize + display images dynamically in response to changes in available space for it. It takes the content-fit property to allow for configuration of how to fit.

But it doesn't allow for configuration of the resize interpolation method, e.g. nearest-neighbor, bilinear. Right now, it always resizes with bilinear interpolation, which makes small images resized larger always fuzzy, with no ability to change.

It is possible to resize the underlying image e.g. pixbuf with nearest-neighbor but this is not the same because the pixbuf would have to anticipate the expected size it would display at.

The picture widget should take an interpolation property, GdkPixbufInterpType or similar, to allow configuration of interpolation method directly.