Fix regression causing pasted images to have a zero-size transform (#2238)

* Use the identity matrix as the default for an image frame

* Fix all usages to be equivalent to their pre-refactor versions, opting to keep ZERO not IDENTITY as the default image size

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Co-authored-by: Keavon Chambers <keavon@keavon.com>

node-graph/gstd/src/raster.rs

@@ -627,7 +627,7 @@ fn mandelbrot(footprint: Footprint) -> ImageFrameTable<Color> {
 			..Default::default()
 		},
 		transform: DAffine2::from_translation(offset) * DAffine2::from_scale(size),
-		..Default::default()
+		alpha_blending: Default::default(),
 	};
 
 	ImageFrameTable::new(result)