Update NamedImage and fix Linux build

[Kyle-Ye]

Summary

• Fix Linux build errors for CoreUI-specific types (CUINamedVectorGlyph, SFSymbols, CGImage.width/height) by adding proper platform guards
• Update NamedImageTests: remove trivial equality/hash tests, add meaningful tests for BitmapKey environment init, size class conversion, fillVariant, findName, and mayContainSymbol logic
• Fix incorrect resolveError test expectation (scale 0 → 1.0)

Test plan

• Verify Linux build passes via ./Scripts/build.sh
• Run swift test --filter OpenSwiftUICoreTests on macOS

[augmentcode]

🤖 Augment PR Summary

Summary: This PR updates the image/symbol pipeline to build cleanly on Linux while improving NamedImage behavior coverage.

Changes:

• Added platform guards and lightweight shims for CoreUI/RenderBox-related types to avoid CoreUI-specific build failures on non-Darwin platforms.
• Updated `DisplayList`/`SymbolEffect`/image code to import `OpenRenderBoxShims` and remove/adjust stubs accordingly.
• Implemented substantial parts of `ResolvedVectorGlyph` setup (animator wiring, environment-driven rendering mode selection, alignment/style helpers).
• Introduced `ImageResolutionContext.effectiveSymbolRenderingMode` and a placeholder `willUpdateVectorGlyph` hook for future transition logic.
• Hardened `NamedImage` decoding and system asset initialization with `canImport(Darwin)` / `canImport(CoreGraphics)` checks.
• Filled in missing font trait mutation for weight/width modifiers.
• Reworked `NamedImageTests` to drop trivial equality/hash assertions and add targeted behavior tests (environment init, size class conversion, fill/name lookup, symbol detection).

Technical Notes: Several new code paths are guarded behind OPENSWIFTUI_LINK_COREUI / OPENSWIFTUI_RENDERBOX, with explicit platform-unimplemented traps where functionality isn’t expected to work yet.

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[augmentcode]

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[codecov]

Codecov Report

❌ Patch coverage is 2.85714% with 102 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.43%. Comparing base (33a74eb) to head (385b96d).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ces/OpenSwiftUICore/View/Image/GraphicsImage.swift	4.54%	63 Missing ⚠️
...enSwiftUICore/View/Image/SymbolRenderingMode.swift	0.00%	21 Missing ⚠️
Sources/OpenSwiftUICore/View/Image/Image.swift	0.00%	13 Missing ⚠️
...ources/OpenSwiftUICore/View/Image/NamedImage.swift	0.00%	3 Missing ⚠️
.../OpenSwiftUICore/View/Text/Font/ModifiedFont.swift	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #808      +/-   ##
==========================================
- Coverage   27.57%   27.43%   -0.15%     
==========================================
  Files         658      660       +2     
  Lines       41277    42376    +1099     
==========================================
+ Hits        11383    11624     +241     
- Misses      29894    30752     +858     

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