wasm: Wrong SVG size if the svg don't have explicit with/height

[hunger]

The latch on the printerdemo looks wrong in Slintpad (1.8.0 version):

On chrome:

In Firefox:

Looks to me like the rendering of the SVG is missing/has the wrong size.

[ogoffart]

Note that this can be reproduced in slintpad, but not on the rust-compiled demo.

I believe the difference is that the rust demo uses resvg to render the SVG, while the interpreter uses a <img> tag with a source being the URL of the .svg

[ogoffart]

The home-automation's padlock icon has the same issue.
The problem appear in the printer demo since commit 0fd9bf4 changed the svg so that it doesn't have a width and height hardcoded in the svg element.

resvg which is what we use to render svg in non-web, uses the size of the viewBox when width and height are not specified.

On the wasm interpreter, we do use an <img> element's naturalWidth / naturalHeight.

slint/internal/core/graphics/image/htmlimage.rs

Line 50 in fc01c54

self.dom_element.natural_width(),

That returns 0 on firefox, and some wrong value with chromium.
I wonder if there is a better way to get the size that uses the viewbox of the svg if width and height are not specified.