* M8: large images on the canvas draw from a smaller copy (#1483)
An image shown smaller than its pixels draws on the canvas from a copy scaled down to 4096 or 8192 px on its longer side, cached beside the image in the same budget. Two 16000 x 10000 images (640 MB each) evicted each other on every frame that drew both; as copies they take 80 MB together zoomed out. Moving one over the other: about 2.1 s a frame before, 11 ms at fit and 15 ms at 30% after. Exports, thumbnails and views at 100% and closer draw from the image itself. Tests in large_image_tests; timings in large_image_bench_tests (ignored).
* M8: drop the ignored large-image benchmark; its numbers are in the PR (#1483)