Add ForegroundStyle and BackgroundStyle support

[Kyle-Ye]

No description provided.

[augmentcode]

🤖 Augment PR Summary

Summary: This PR adds end-to-end support for context-driven ForegroundStyle and BackgroundStyle rendering in OpenSwiftUI, including environment plumbing and snapshot UI coverage.

Changes:

• Implemented BackgroundStyle resolution, including environment keys for background overrides and background grouping/layering state.
• Added View.backgroundStyle(_:) plus internal helpers _addingBackgroundGroup() / _addingBackgroundLayer() to influence default background behavior.
• Implemented View.foregroundStyle overloads (single/pair/triple) and corresponding primitive modifiers that write resolved styles into the environment.
• Updated foreground-style resolution defaults to use hierarchical primary style behavior when no explicit style exists.
• Completed OffsetShapeStyle multi-level .resolveStyle handling and removed the now-redundant standalone ForegroundStyle modifier file.
• Introduced new shape-style helpers (ShapeStylePair, ShapeStyleTriple, InterpolatedShapeStyle) to support multi-level and animated style packs.
• Added snapshot UI tests validating default and nested foreground/background style behaviors.

Technical Notes: Style resolution is driven via _ShapeStyle_Shape operations and produces _ShapeStyle_Pack entries for requested level ranges, enabling hierarchical style selection and animation via pack AnimatableData.

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[augmentcode]

Review completed. 2 suggestions posted.

Comment augment review to trigger a new review at any time.

[augmentcode]

systemBackgroundColor(info:context:scheme:)’s .light branch ignores info.layer, so _addingBackgroundLayer() won’t affect the computed background color in light mode (only in .dark). If layers are meant to model the system’s “secondary/tertiary background” behavior, you may need to incorporate info.layer into the light-mode calculation too.

Severity: medium

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[augmentcode]

In BackgroundStyle._apply’s generic .resolveStyle(name, levels) case, reading innerShape.stylePack[name, 0] assumes the inner application wrote at level 0; if levels.lowerBound isn’t 0 (e.g. via offset(by:)), this will likely read .clear and populate incorrect entries. Consider indexing using the level actually written (like levels.lowerBound or level) so offset ranges resolve correctly.

Severity: medium

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 312 lines in your changes missing coverage. Please review.
✅ Project coverage is 13.04%. Comparing base (9916291) to head (0be3007).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...nSwiftUICore/Shape/ShapeStyle/ShapeStylePair.swift	0.00%	88 Missing ⚠️
...SwiftUICore/Shape/ShapeStyle/BackgroundStyle.swift	0.00%	86 Missing ⚠️
...SwiftUICore/Shape/ShapeStyle/ForegroundStyle.swift	0.00%	70 Missing ⚠️
...Core/Shape/ShapeStyle/InterpolatedShapeStyle.swift	0.00%	44 Missing ⚠️
...wiftUICore/Shape/ShapeStyle/OffsetShapeStyle.swift	0.00%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #785      +/-   ##
==========================================
- Coverage   13.13%   13.04%   -0.09%     
==========================================
  Files         620      621       +1     
  Lines       36773    37040     +267     
==========================================
+ Hits         4829     4831       +2     
- Misses      31944    32209     +265     

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