Intrinsic sizing for inline SVG; viewport re-resolution and clipping for SVG content; img/object dimension attributes

[nicoburns]

Summary

Builds on #639 and #643 (img/object dimension attribute mapping, now the base branch of this PR). This PR fixes how replaced SVG (and img) elements are sized and painted. #642 (stacked on this PR) adds viewport re-resolution for viewBox-less SVG; together with #643 they make css/CSS2/normal-flow/block-replaced-height-001/002/004/005/006/007 pass and a full-suite comparison vs main shows 51 tests fixed, 3 regressed (regressions analysed below).

Inline SVG intrinsic sizing (layout/mod.rs, node/element.rs)

SvgImageData previously exposed only usvg::Tree::size(), which conflates "declared absolute dimensions" with usvg's fallbacks (percentages resolved against 100x100, viewBox size, etc.). New accessors preserve what the root <svg> actually declared:

• intrinsic_width()/intrinsic_height(): Some only for absolute (non-percentage) width/height attributes
• viewbox_aspect_ratio(): ratio from the viewBox when dimensions are missing
• resolved_width()/resolved_height(): inline-<svg>-only resolution where percentage attributes resolve against the containing block

The replaced measure function now receives a correct inherent_size/inherent_ratio for SVG instead of usvg's fallback size, so CSS2's intrinsic-sizing rules (ratio transfer, 300x150 default) apply per spec.

SVG content clipping (render.rs)

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).

Remaining known regressions (3)

• css/css-rhythm/replaced-elements/block-level-{img,canvas}-margins-affected-by-block-step-size.html: these passed on main only because replaced elements were stretch-sized to the 100px container. With correct intrinsic sizing they need actual block-step-size support to pass.
• css/css-lists/list-item-definition.html: display: list-item on <svg>/<img> plus ::before/::after list-item markers; the previous pass was accidental (test and ref both rendered identically wrong). Needs marker-box work unrelated to replaced sizing.

WPT results

52 newly passing, 5 newly failing (net +47).

Full diff (57 changed tests)

+ Fail => Pass css/CSS2/backgrounds/background-001.xht
+ Fail => Pass css/CSS2/backgrounds/background-002.xht
+ Fail => Pass css/CSS2/backgrounds/background-003.xht
+ Fail => Pass css/CSS2/backgrounds/background-006.xht
+ Fail => Pass css/CSS2/backgrounds/background-007.xht
+ Fail => Pass css/CSS2/backgrounds/background-008.xht
+ Fail => Pass css/CSS2/backgrounds/background-009.xht
+ Fail => Pass css/CSS2/backgrounds/background-010.xht
+ Fail => Pass css/CSS2/backgrounds/background-014.xht
+ Fail => Pass css/CSS2/backgrounds/background-018.xht
+ Fail => Pass css/CSS2/backgrounds/background-022.xht
+ Fail => Pass css/CSS2/backgrounds/background-087.xht
+ Fail => Pass css/CSS2/backgrounds/background-182.xht
+ Fail => Pass css/CSS2/backgrounds/background-328.xht
+ Fail => Pass css/CSS2/backgrounds/background-329.xht
- Pass => Fail css/CSS2/backgrounds/background-attachment-applies-to-007.xht
- Pass => Fail css/CSS2/backgrounds/background-attachment-applies-to-009.xht
- Pass => Fail css/CSS2/backgrounds/background-attachment-applies-to-012.xht
- Pass => Fail css/CSS2/backgrounds/background-attachment-applies-to-013.xht
- Pass => Fail css/CSS2/backgrounds/background-attachment-applies-to-014.xht
+ Fail => Pass css/CSS2/backgrounds/background-image-cover-002.xht
+ Fail => Pass css/CSS2/backgrounds/background-image-cover-004.xht
+ Fail => Pass css/CSS2/backgrounds/background-image-cover-attachment-001.xht
+ Fail => Pass css/CSS2/backgrounds/background-image-transparency-001.xht
+ Fail => Pass css/CSS2/backgrounds/background-repeat-001.xht
+ Fail => Pass css/CSS2/backgrounds/background-repeat-002.xht
+ Fail => Pass css/CSS2/backgrounds/background-repeat-003.xht
+ Fail => Pass css/CSS2/backgrounds/background-repeat-005.xht
+ Fail => Pass css/CSS2/borders/border-bottom-width-003.xht
+ Fail => Pass css/CSS2/borders/border-bottom-width-025.xht
+ Fail => Pass css/CSS2/borders/border-bottom-width-058.xht
+ Fail => Pass css/CSS2/borders/border-bottom-width-069.xht
+ Fail => Pass css/CSS2/borders/border-bottom-width-080.xht
+ Fail => Pass css/CSS2/borders/border-top-width-003.xht
+ Fail => Pass css/CSS2/borders/border-top-width-025.xht
+ Fail => Pass css/CSS2/borders/border-top-width-058.xht
+ Fail => Pass css/CSS2/borders/border-top-width-069.xht
+ Fail => Pass css/CSS2/borders/border-top-width-080.xht
+ Fail => Pass css/CSS2/borders/border-width-shorthand-001.xht
+ Fail => Pass css/CSS2/borders/border-width-shorthand-002.xht
+ Fail => Pass css/CSS2/borders/border-width-shorthand-003.xht
+ Fail => Pass css/CSS2/borders/border-width-shorthand-004.xht
+ Fail => Pass css/CSS2/floats-clear/float-replaced-width-011.xht
+ Fail => Pass css/CSS2/inline-svg-100-percent-in-body.html
+ Fail => Pass css/CSS2/normal-flow/block-replaced-width-006.xht
+ Fail => Pass css/CSS2/normal-flow/inline-block-replaced-width-006.xht
+ Fail => Pass css/CSS2/normal-flow/inline-replaced-width-006.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-006.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-013.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-020.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-027.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-034.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-069.xht
+ Fail => Pass css/CSS2/positioning/absolute-replaced-width-076.xht
+ Fail => Pass css/css-borders/corner-shape/corner-shape-svg-border.html
+ Fail => Pass css/css-images/object-position-svg-001i.html
+ Fail => Pass css/css-images/object-position-svg-002i.html

_{Generated by the WPT workflow.}

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

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