fix(addon-image): use device pixel dimensions for HiDPI rendering

[mgabor3141]

The image addon canvas is sized using CSS pixel dimensions, ignoring devicePixelRatio. On HiDPI displays images render at lower resolution, appearing blurry.

Fix: use dimensions.device.* for the canvas backing store and all draw/clear coordinates, while setting canvas.style.width/height to CSS dimensions for display sizing.

Fixes #5035

[jerch]

@mgabor3141 I looked at your PR - You sure this works correctly and prints the image at the correct size? You basically just increased the canvas internal size, so with a DPR of 2 wouldn't images get rendered half as big?

Don't we need a transform or scale adjustment on the context like this:

ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
// or
ctx.scale(dpr, dpr);

Note that we have to stay in the DPR 1 assumption for image pixels, as image sequences currently have no way to tell us that a different DPR was targeted. Thus an image pixel must be treated as one CSS pixel.

Edit: Another way would be to do the CSS --> device pixels resizing on the image prehand, this way we would get less rounding artifacts (given that DPR is usually >1).