Clip SVG replaced content, except SVGs that blend with their backdrop

[nicoburns]

Summary

Rebased on latest main; the intrinsic SVG sizing and img/object dimension-attribute work originally in this PR has since landed on main (e.g. #606, #643, #662), so what remains is the SVG content clipping fix.

SVG elements now participate in replaced-content clipping like raster images (fixes overflow bleed in e.g. css/CSS2/positioning/absolute-replaced-width-003b.xht and css/css-overflow/display-flex-svg-overflow-default.html). Exception: an SVG containing backdrop-blending groups (mix-blend-mode mapped by usvg) is not clipped, since the isolated buffer of a clip layer would make the blend composite against transparency instead of the page backdrop (css/compositing/mix-blend-mode/mix-blend-mode-svg.html):

fn blends_with_backdrop(group: &usvg::Group) -> bool {
    group.blend_mode() != usvg::BlendMode::Normal
        || (!group.isolate() && group.children().iter().any(/* recurse into groups */))
}
let is_svg = element.svg_image_data().is_some_and(|data| !blends_with_backdrop(data.tree.root()));
let is_image = is_svg || element.raster_image_data().is_some();

Also adds an ElementData::svg_image_data() accessor returning the full SvgImageData (used by #642, which is stacked on this PR).

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/51256d0b440341bd874c6dc59e138478
Requested by: @nicoburns

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