Ensure that we never round the canvas dimensions above `maxCanvasPixels`
by rounding them to the preceeding multiple of the display ratio rather
than the succeeding one.
This commit introduces a test to ensure that:
- When zooming below the maxCanvasPixels limit, the canvas is rendered
with the correct size (the two sides are multiplied by the zoom factor).
- When zooming above the maxCanvasPixels limit, the canvas size is capped.
This parameter allows defining which point should remain
fixed while scaling the document. It can be used, for example,
to implement "zoom around the cursor" or "zoom around
pinch center".
The logic was previously implemented in `web/app.js`, but
moving it to the viewer scaling utilities themselves makes it
easier to implement similar zooming functionalities in
other embedders.
This commit adds a test for 0603d1ac18.
Before the fix the `pagerendered` events would be fired just 2-3
milliseconds after the call to `increaseScale`/`decreaseScale`.
