Add blur filter rendering support

[Kyle-Ye]

Close #880

Agent Summary

This PR adds the filter plumbing needed for blur rendering in the display-list renderer.

• Adds a QuartzCore filter bridge and Swift-side conversion from GraphicsFilter into layer filters.
• Updates display-list merge behavior for filter and transform effects so renderer state tracks the expected requirements.
• Adds shared UI coverage for blur and variable blur, including a SwiftUI SPI interface entry used by the SwiftUI-backed example and tests.

[augmentcode]

🤖 Augment PR Summary

Summary: This PR adds display-list renderer plumbing to support blur (including variable blur) via QuartzCore filters.

Changes:

• Introduces a CAFilter private bridge (C/ObjC shims) and Swift conversions from GraphicsFilter to layer filter arrays.
• Moves/centralizes graphics-related conversion helpers into a new GraphicsConversions module file (e.g., blend mode + frame-rate range utilities).
• Updates display-list merge behavior for effects (filters/transforms/groups) so renderer state and view requirements better reflect actual rendering needs.
• Adds snapshot UI coverage for blur and variable blur, plus a small shared example view used by tests.
• Extends the SwiftUI SPI interface to expose View.variableBlur(maxRadius:mask:opaque:) on supported OS versions.

Technical Notes: Filter application now routes through CoreViewSetFilters using CAFilter instances built from GraphicsFilter, and group-name handling is updated for backdrop grouping.

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[augmentcode]

Review completed. 2 suggestions posted.

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 13.78%. Comparing base (aa8f2c0) to head (049150d).

Files with missing lines	Patch %	Lines
...Core/Render/DisplayList/DisplayListViewModel.swift	0.00%	33 Missing ⚠️
...urces/OpenSwiftUICore/Graphic/GraphicsFilter.swift	0.00%	32 Missing ⚠️
.../OpenSwiftUICore/Graphic/GraphicsConversions.swift	0.00%	2 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (aa8f2c0) and HEAD (049150d). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (aa8f2c0)	HEAD (049150d)
	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #882       +/-   ##
===========================================
- Coverage   26.95%   13.78%   -13.17%     
===========================================
  Files         678      639       -39     
  Lines       47144    41357     -5787     
===========================================
- Hits        12706     5700     -7006     
- Misses      34438    35657     +1219     

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